If you are new to Drupal 7 and are creating views, there are lot of changes in what is exposed in the filters. One of the reasons is because Drupal 7 uses views 3.

One example is if you want to create a view of content and you want to add current user as a filter so the uses only see their content. 

Unlike previous versions of views, first you will need to define a relationship with Content: User. Now the User: current will be exposed in the filter which you can use to filter the content on current user.