How do I join a clan?

To find a clan to join, you have to reach level 30 first.
Clans can be open, invite only (requiring an invitation to join), request (requiring a request to be sent).
Type the name of the clan your are willing to join or choose one of those available in the list.
Please note, that a player can send only one request to a certain clan. A new request sent to the same clan will cancel the previous one. After leaving a clan you'll have a 24-hour cooldown before joining a new one.

How do I leave a clan?

Open the "Clan" menu (next to the Settings button in the upper right corner of the screen) and choose the "Members" tab, tap the button "Leave clan" to the right from your nickname. Please also note that you cannot delete or rename a clan.