You can join any public group in Nitoku. Go to the team that you want to join and click on the Members tab, on that tab you will find the Join Team icon, click on that icon and you will start following the team. After you are a follower of a team, the team will be included on your public teams and you will be able to edit the pages of the team and send change requests. If you at some point decide to leave the group, on the same Members tab, click on the Leave Team icon.
You can only join private teams after the team's owner has sent you and invite to join. You will receive the invite on your notifications, after you receive this notification you can join the team or ignore the invite, if you want to join the team just click on the "Follow team" icon of the notification. If you at some point decide to leave the group, go to the Members tab of this team and click on the Leave Team icon.