how do I join a clan ?

You are invited to one, and you accept their invite.

You get a notification on your email if you get invited except you got that option disabled.

You can join clans directly if you visit their clan page on "community->clans->pick one you like". To join you need always an invitation first.

First:

Look on the clan list for a clan you like

message the owners of the clan

get an invite

go on clan page and accept invite.

rule the world.