The ls program prints human-readable listings of directories. By default, with no arguments, this list is just the names of each file in the current directory, printed horizontally for readability:

$ ls
books  documents  music

If we add the -a flag, we can include dot files in our output, files beginning with a period:

$ ls -a
.  ..  .bashrc  .profile  books  documents  music

Note that this output includes the  . and .. entries, referring to the current and parent directory, respectively.

Using the -l option, which can be combined with -a, we can get a long listing of files:

$ ls -al
drwxr-xr-x 91 bashuser  bashuser  16384 Jul  7 19:50 .
drwxr-xr-x  5 root      root       4096 Jun  1 20:28 ..
-rw-r--r--  1 bashuser  bashuser   3391 Jun 30 01:03 .bashrc
-rw-r--r--  1 bashuser  bashuser    571 Jun 30 01:03 .profile
drwxr-xr-x 54 bashuser  bashuser   4096 Feb  6 14:54 books
drwxr-xr-x  2 bashuser  bashuser   4096 Nov 29  2014 documents
drwxr-xr-x 33 bashuser  bashuser   4096 Jun  4 00:06 music

Which columns are returned and the format the data takes varies depending on which options you provide, the system's configuration, your personal configuration, and which version of ls is installed.