To protect your Tableau Server contents, you can click on the three dots ... on any element (Project, Workbooks, Views, or Data Sources) to show the options and select Permissions. When you click on Permissions, Tableau opens a new window where you can specify many security options.

Here's the Permissions menu:

On this menu, you'll always see the All Users permissions. You can click on the dots to edit them. You can also click on Add a user or group rule to specify new permissions for specific Users or Group. When you edit the permissions, you can see, for each element, a list of pre-configured roles.

If you click on the arrows next to an element (Project, Workbooks, or Data Sources), you get more detail and the possibility to edit each permission individually. Each Permission can be allowed (green), denied (red), or unspecified (grey). To edit an individual Permission, click on its box. 

Here's an example of a Permissions edition with a detailed view for Workbooks:

Know that all options are not available for all elements. Here's the complete list of Permissions, grouped by elements where they appear:

• Global permissions:
  • View : Specifies whether a user can see the element
  • Save : Overwrites the existing element on the server
• Project permissions:
  • Project leader : Someone with a project leader Permission has all Permissions on that project
• Workbook and Data Sources Permissions:
  • Download /: Downloads the Data Source or the Workbook
  • Delete : Removes the element from the server
  • Set Permissions : Gives us the ability to change and define the Permissions
• Workbook Permissions:
  • Download image : Downloads an image of the visualization
  • Download summary data : Downloads a summary of the data in a visualization
  • View comments : Sees the comments posted under a visualization
  • Add comments : Adds comments under a visualization
  • Filter : Uses the Filters available and the Keep Only and Exclude features
  • Download full data: Downloads the complete data used in a visualization, with all the rows and columns 
  • Share customized: Gives us the ability to create and share a customized view
  • Web edit : Opens the Tableau Server edition window where a user can modify the visualization or create new ones
  • Move : Changes the Project of a Workbook

• Data Sources Permissions:
  • Connect: Gives us the ability to connect to the Data Sources to create further analysis on Tableau Server or Tableau Desktop

With those Permissions, you can control who has access to what on Tableau Server. You can, for example, allow only a few users to access your Workbook. But what if you want to control what those users can see? Let's say that, based on the Sample-Superstore Data Source, you want to control the Region that the users can see. To do that, you need to set a User Filter.