When a permission is set to Team only, users can only access records owned by or assigned to users in the team for that specific permissions.
When a user requires access to another team's records or content, an Admin with the Add and edit users permission, or a Super Admin, can assign a user to additional teams. They'll then be able to access the additional team's records and content with Team only permissions. Additional team members can also access primary team members' owned contacts.
When a user is added to an additional team:
the user can access the additional team's records and any content that's set to Team only permissions.
the user can access primary team members' owned records.
the primary team members can access the additional team member's records.