HELP!!!!

You usually just have to find one that's open, which is a battle in itself. Just try sending a message to the teams, telling them you'd really like to join if there are any open positions.
There is no official "team" sort of function on this website. It's usually just a group of people that get together, make a page on the forum, split into teams, and then compete against the other teams with weight loss and challenges and stuff.

Basically, find an open team, usually on the "Motivation" forum section, or if you can't find any open ones (if they are closed, they ususally state that on the forum title), start sending messages to the leaders of the team (usually the first person to start the board).

bump

You can also contact the leader of the challenge and see if they will put you on a waiting list. Usually there are plenty of people trying to get in after the challenge is full and becomes closed. People drop out all the time and you have a fair chance of getting in.