Your teammates can be given different permissions according to the access level you'd like them to have. This is an overview of the options and what each role entails. You can change these permissions by clicking the 'Team settings' icon in the sidebar within the app.
The person who first sets up a Team is automatically the Owner. This person is responsible for billing and is able to access all projects within the Team and administer teammates (invite new teammates, change roles and remove teammates). Teams may only have one Owner.
People given an Admin role can do everything an Owner can do, except access billing. Teams may have as many Admins as they need.
Members can see all projects within the Team, and will be able to see all new projects that are created, and create new projects within the Team. They aren't able to administer teammates.
Restricted Members cannot see Team projects by default, but have to be manually added to each project. Restricted Members can create new projects within a Team. If you want someone to only be able to see a few projects, add them as a Restricted Member.