Teams are managed groups of users that can be added to projects just like collaborators.
Start by navigating to the Collaborators tab, then Teams, and "Create New Team".
Next, enter a Team Name and select the Project or Projects that them Team will have access to. The last step is to click "Add Collaborator" which will open a dropdown of existing Collaborators to choose from to add to the project.
If no other Collaborators exist for you to add you must first add collaborators by navigating back to the Collaborators tab and click "Add Collaborator".