By using target audiences, you can display content such as list or library items, navigation links, and entire web part to specific groups of people. This is useful when you want to present information that is relevant only to a particular group of people.
Any item in a SharePoint list or library can be targeted to specific audiences.
In addition, you can target site navigation links to audiences. Targeting the links simplifies the users’ experience, because they see only the navigation links that are relevant to them.
Target a navigation link to an audience
- On the Web page that contains the site navigation, on the site actions menu, click Site Settings and then click Modify Navigation.
- On the Site Navigation Settings page, click add link
- In the Navigation Link dialog box, type the title and URL of the link, and then add one or more audience names to the Audiences list.
Target a Web Part to an audience
- On the Web page that contains the Web Part, on the site actions menu, click Edit Page.
- On the Web Part, click the edit menu , and then click Modify Shared Web Part.
- Under Advanced, add one or more audience names to the Target Audiences list.
For more Info see http://office.microsoft.com/en-us/sharepointserver/HA101690531033.aspx