If a friend has set up a team and you'd like to join you may do so both (a) if you have not yet purchased your entry and (b) if you have purchased your entry but want to join a team.
(a) If you want to sign up and join a team at the same time, simply begin typing the name and select the team you'd like to join in the 'Select Team' field, at checkout. You may need a password if one has been created by the Team Captain.
(b) If you have already entered an event as an individual but want to join a team, you can do this by going to the 'My Entries' section of your Dashboard, selecting 'Edit Entry' which you will find in 'Entry Actions' next to your ticker. Then find the team you'd like to join and click 'UPDATE ENTRY'.