There is an overview of several reports in the Process Guidance.

From VS: In Team Explorer expand your project -> expand Documents -> Expand Process Guidance -> Open ProcessGuidance.html

Select Index from the tabs at the top of the page.
Select Reports from the menu on the left.

For an Agile project this will describe the following reports:

Actual Quality versus Planned Velocity
Unplanned Work
Velocity
Bug Rates
Bugs by Priority
Reactivations
Quality Indicators
Remaining Work

Hopefully this can get you started.