Team Web Access in Team Foundation Server 2012 (and Team Foundation Service) has been completely redesigned and contains some great new agile planning features.  However, some of the features, Backlog Management, Sprint Planning and Feedback Requests specifically, require you to have a copy of Visual Studio Premium, Ultimate or Test Professional (anything above Visual Studio Professional).

Compare Visual Studio 2012 editions

However, even if you have the correct version of Visual Studio installed you will still not see the additional features without adding your account to the correct group in Web Access.

Features Accessed Through Web Permissions
http://msdn.microsoft.com/en-us/library/jj159364

There are three levels of account for Web Access and by default you will have a "Standard" account.

• Limited. This Work Item Only View (WIOV) allows a user to create any type of work item and view or edit any work items they have created.
• Standard. Members of this group can view the home pages for teams that they belong to. They have quick access links to the task board, team favourites, work items, and all features except feedback and backlog views.
• Full. Members of this group can view all of the Standard features, plus backlog and feedback view. They have quick access links to all activities.

Permissions can be changed through the Web Access Control Panel:

Your Team Web Access experience will depend on your account level.

With no client access license (Limited) you get this view:

With Visual Studio Professional or a Standard CAL (Standard) you get this:

And with Visual Studio Premium/Ultimate (Full) you get this.

Richard