The "Team Members / Activity" tab provides an area to add additional team members outside of the Project Manager and Salesperson already assigned to the Project. Team Members will show up in Project grids such as Current Opportunities and Actions to Perform so you can filter down when necessary to your name. You also have the ability to access a Project activity report in the "Last Accessed By" section as highlighted below to see who has been in the selected Project, when, how long, from what computer, etc.
...