The Team area (under Settings → Team) is where you add the people who work in your workspace and manage what they can do.
Roles determine what each member can see and do across the modules. Grant the least access someone needs for their job, and adjust it as their responsibilities change. Removing a member revokes their access to the workspace.
Note: for the Help Desk specifically, being in the workspace isn't enough to see a particular help desk's tickets — members are added to each help desk individually (see the Help Desk section).