The Staffing tab is located on a project. It contains the Team Builder, Resource Grid, and People sub-tabs. Each of these have different functions, but all aid in the development and support of the project team.
You can easily communicate with users on your project by using the People subtab. You can send updates to the whole project team or to select team members.
You can also tag other users in your updates. For more information about tagging other users, see "Including Others on Updates."