You might know what hat you wear in your organization, but do you know your role-that is, when it comes to using Project Web Access? A good starting point might be the Project Web Access role guides, which are an overview of all the features available to you, categorized by your role in your organization. An executive, for example, will probably be more interested in reporting features than team members, who may be more interested in recording the time spent working on project tasks. And an administrator will probably be interested in making sure all the features are working correctly in order to keep everybody happy and productive.
These role guides can help you figure all this out. See a list of them all at http://office.microsoft.com/en-us/projectserver/HA102513961033.aspx?pid=CH101477201033.