If you've been designated as an administrator of the Team account - you can log into your account page and personalize the group settings:

From this panel, the administrator can add new users, remove users fro the group, change a user's role (member/admin) and see when a user last interacted with the shared library. 

You can then invite the user via their e-mail address, and select if you'd like for them to be a member or an admin. Invited users will get a welcome email and be prompted to set-up their account. 

Questions? Contact us at Support!