Users connect to the Internet through a variety of methods. A relatively inexpensive but slow way to connect is with dial-up service, which involves using a modem and a phone line. Faster ways to connect include DSL (Digital Subscriber Line), cable modem, satellite, and fiber-optic access. Networks include special wireless transmitters that allow computers to access the Internet wirelessly. Companies that help you connect to the Internet are known as Internet service providers, or ISPs.

Connection speeds play an important part in a user's Internet experience because slower connections result in slower file transfers and Web page viewing. Dial-up connections offer the slowest access to the Internet at up to 56 kilobits per second, or Kbps. DSL usually offers connection speeds of up to 3 megabits per second, or Mbps, whereas cable modems can achieve speeds of up to 30 Mbps. A Web page that takes about 20 seconds to download via dial-up can take less than a second using a cable modem.

The Internet infrastructure relies on a variety of protocols that dictate how computers and networks talk to each other. For example,Transmission Control Protocol/Internet Protocol, or TCP/IP, is a set of rules that control how Internet messages flow between computers.Hypertext Transfer Protocol, or HTTP (

The World Wide Web is a giant collection of documents, or pages, stored on computers around the globe. Commonly called the Web, this collection of pages represents a wealth of text, images, audio, and video available to anyone with a computer and an Internet connection. Web pages are stored on servers, which are Internet-connected computers running software that allows them to serve up information to other computers. When you place a text file, image, or other document in a special Web directory on a server, that information is available for other Web users to view. Chapter 13 talks about how to transfer information to a Web server.

Every page on the Web has a unique address called a URL, which is short for Uniform Resource Locator. A URL looks like this:

http://www.example.com/index.html

If you know a page's URL, you can type it into a Web browser to view that page over the Internet. You can also view pages by way of hyperlinks, or links, which are clickable words or images on Web pages. Every link on a Web page is associated with a URL that connects it to another page, media file, or other resource on the Internet. Users can jump from one Web page to another by clicking links. Chapter 6 discusses how to create links with HTML.

A Web browser is software that allows you to view and interact with Web pages. When you type a URL or click a link in a Web browser, the browser retrieves the appropriate page from a server on the Internet and displays that page. Microsoft Internet Explorer, Mozilla Firefox, and Apple Safari are the three most popular browsers in use today. Each program has evolved through a number of versions, with newer versions supporting more recent Web features. As you build your pages using HTML code, remember that different browsers may display your pages slightly differently depending on the version.

HTML consists of text interspersed with special instructions known as tags. Surrounded by brackets, < >, HTML tags tell a browser how to organize and present text, images, and other Web page content. Many tags are written using an opening tag and a closing tag that surround content that appears on the page. When writing HTML tags, you can use upper- or lowercase letters. To make the coding easy to distinguish from other text in the page, you can type tag names in uppercase. For details, see the section "Understanding HTML Syntax."

When a browser displays a Web page, it retrieves the HTML file for that page from a server, parses the HTML tags to determine how the content should be formatted, and renders the page. The HTML tags tell the browser what images, video, audio, and other content need to be downloaded and integrated into the page. The HTML may also tell the browser to download style sheets and interactive scripts to further enhance the page. To view the HTML underlying a Web page, see the section "View HTML Code in a Browser."

The World Wide Web Consortium, or W3C, is the primary group guiding the evolution of the HTML language. The W3C is made up of hundreds of companies and organizations including Web industry leaders such as Microsoft, Apple, and Google. The standards developed by the W3C give developers of Web servers and browsers a set of common guidelines with which to develop their products. You can visit the W3C's Web site at www.w3.org.

The most recent version of HTML is 4.01. Version 4.01 includes rules for using more than 90 different HTML tags, most of which are covered in this book. It improves on previous versions by adding better support for multimedia, scripting, and style sheets. Support for style sheets is especially important because it allows developers to apply more precise formatting to Web pages. It also allows developers to keep complex styling information separate from the rest of the HTML. Style sheets are covered in Chapters 9, 10, and 11.

XHTML, or Extensible Hypertext Markup Language, is an alternative language for coding Web pages that conforms to the stricter standards of XML, or Extensible Markup Language. XHTML is tag-based and uses many of the same tags as in HTML. However, in XHTML, all tags must be closed, tag names and attributes must be coded in lowercase, and attribute values for tags must be surrounded by quotes. Most modern browsers can read both HTML and XHTML. Although XHTML is not covered in this book, you can read more about it at the W3C site at www.w3.org.

As this book is being published, the W3C is developing the specifications for HTML 5, the next version of HTML. This version introduces features to help Web designers more easily create and maintain the dynamic pages seen in many of today's Web sites. HTML 5 will include tags for defining headers, footers, and navigation sections, along with tags for adding interactive elements such as editable and sortable tables. For more information, see www.whatwg.org/html5.

Most computer operating systems come with a Web browser already installed. Microsoft Windows Vista computers include the Internet Explorer browser, whereas Apple Mac computers include the Safari browser. (The examples in this book use Internet Explorer.) Mozilla Firefox is another Web browser that has become increasingly popular in recent years. You can learn more about Firefox and download it for free at www.mozilla.com/firefox. For more information about the Web browsers in use today, see the Wikipedia entry at http://wikipedia.org/wiki/Web_browser.

There are many Web browsers in use today, and numerous versions of each. Although most of them interpret HTML essentially the same way, slight differences in interpretation mean that not all of them display Web pages exactly the same way. Also, some more recent browser versions recognize newer HTML features that older browsers do not. You can avoid surprises by writing clean, well-formed HTML code and testing your pages in different browsers as you work. Wikipedia offers a detailed comparison of Web browser features at http://wikipedia.org/wiki/Comparison_of_web_browsers.

Simple text editors, also called plain-text editors, are easy to find. Microsoft Windows Vista comes with Notepad, whereas Apple Mac computers come with TextEdit. Simple text editors offer no-frills word processing and are often the best choice when you are learning to write HTML. This book uses the Windows WordPad and Notepad text editors in its examples. Wikipedia has a list of free and commercial text editors at http://wikipedia.org/wiki/List_of_text_editors.

HTML editors, such as Adobe Dreamweaver and Microsoft Expression, are dedicated programs for writing HTML code and managing Web pages. These programs can shield you from having to write HTML code by offering a graphical environment for building Web pages as well as a text-based environment. Most HTML editors also color your HTML tags for easier viewing, validate your code, and help you upload finished pages to a server.

You can also use word processing programs, such as Microsoft Word, to write HTML. In Word, you can select HTML as the file type when you save a document, and the program automatically adds the appropriate HTML tags. However, commercial word processors tend to store lots of extra information with your HTML, which can make it a challenge to edit the files in other editors.

In HTML, tags determine how page content is organized and formatted. Tags consist of words or abbreviations surrounded by angle brackets, < >. This HTML code creates a paragraph in your page:

<P>Hello, world!</P>

Tags can be written using upper-or lowercase letters. The following are all legal versions of the line break tag:

<BR> <br> <Br>

You can type tag names in uppercase to distinguish the code from other text. Uppercase tag names is the convention used in this book. Because Web browsers read the tags as instructions rather than page content, the bracketed information does not appear in the browser window when the page is rendered.

Certain structural HTML tags identify different parts of your HTML document. For example, the <BODY> and </BODY> tags surround the main body content that appears in the browser window. The <HEAD> and </HEAD> tags surround accessory information, including references to style sheets and metadata, that does not appear directly in the browser window. The <HTML> and </HTML> tags appear at the very beginning and very end of the document, respectively. Many tags, such as the paragraph tag <P> and </P>, are written using an opening tag and a closing tag, whereas others, such as the image tag (<IMG>), stand alone. Closing tags must always include a slash (/) before the tag name.

HTML includes a variety of tags for formatting text. You can surround text with <B> and </B> tags to turn text bold and <I> and </I> tags to turn it italic. You can label passages of text with heading tags, which create bold text set off on a separate line. There are six sizes of headings, with <H1> headings being the largest and <H6> headings being the smallest. Text formatting tags are covered in Chapters 3 and 4.

Among the central features of Web pages are the hyperlinks that allow you to navigate from one page to another and one site to another. The <A>, or anchor, tag lets you define text or other page elements as clickable hyperlinks (see Chapter 6). You can organize page content into rows and columns using table tags, which include <TABLE>, <TR>, <TD>, and others (see Chapter 7).

Each HTML tag has specific attributes that you can assign to customize its behavior. Most attributes work by setting a numeric or descriptive value. For example, you can set a paragraph's alignment using the ALIGN attribute and a type of alignment: left, right, center, or justify. The code for a centered paragraph:

<P ALIGN="center">My centered text.</P>

Some attributes are required for an HTML tag to function properly. Attributes always go inside the opening HTML tag, and it is good form to enclose attribute values in quotation marks. The <IMG> tag requires a SRC attribute so that the browser can insert the correct image file on the page:

<IMG SRC="myphoto.jpg">

You can add special characters to a page, such as a copyright symbol or a fraction, by using special codes called entities. Entities represent characters not readily available on the keyboard. All entities are preceded by an ampersand (&) and followed by a semicolon (;). For example, the following code adds a copyright symbol to your page:

©

Entities are also useful for displaying characters that have special meaning in HTML. For example, to create a less-than symbol on your Web page, you use the following code:

<

You cannot use a plain less-than symbol (<) because in HTML it is used to start a tag. For more about entities and special characters, see Chapter 3.

To avoid HTML errors, proofread your code. Most HTML editors have features that highlight bad syntax. Make sure your tags have brackets, your closing tags include a slash, and your attribute values are surrounded by quotation marks. Multiple HTML tags should be properly nested, meaning your closing tags should be in the reverse order of the opening tags. For example:

<P><B>My text.</B></P>

To help make your HTML readable, consider using new lines to type code instead of running everything together on one long line. Doing so will not affect how your page is displayed because Web browsers ignore extra white space. Testing your Web pages in multiple Web browsers can also be a good way to discover syntax errors because browsers can vary in their leniency to certain types of errors.