BLARG, my comment was deleted!
For other users: just go to the user page who you want to make a team with and click "Create Team." If you want to join an existing team, you must contact someone who is already on it and ask them to invite you.
Since teams are created by users who want to pair up, you cannot join an existing team without being invited.
And as for your FAQ suggestion, that's a great idea! I will start putting one together today!