On the Team-Mapping screen you can map piplanning app teams to Rally Projects. This defines into which project in Rally the sticky notes of the piplanning app will be synced to.
If your Rally is setup in a way that you have required fields (except for the Name, Schedule-State and Project fields) for certain Work-Items (Like UserStories), you will need to define a default value for these fields. If you do not define default values, the piplanning app will not be able to create the Work-Items in Rally for you. Keep in mind, that those default values only apply for stickies which were created on the teamboard.