To invite members to a team, you must be the ADMIN (the individual who made the team).
1) Click on the Team that you want to invite people to.
2) Click on USERS.
3) Click on the "here" link found in the first bullet.
4) Enter the email address and click SEND INVITATION.
5) Depending on what email client you are using, an email should open pre-populated with copy that you can send the invitation to.