Our video tutorial found here covers team creation and inviting people to your team.
Only a team 'Admin' (the person who created the team) can invite new users to join their team.
In order to invite new users, you must go to the 'My Team' page and select the "Invite More" button.
At the bottom of the team box, it will state how many users can join your team. If you reach this limit, you will be unable to invite anyone else without cancelling some of the existing pending invites.