Simply go to event page and click register, login via Facebook or google. Now you will get two options:
a) Register as a team leader
b) Register under a team.
Choose the appropriate option. Suppose you chose to register as a team leader, then you have to provide the team name and you will receive a team code, Share the same with your team-mates and ask them to register under a team, they will be asked to enter team code, and confirm team leader, notifications will be sent via email.