You can join a clan by:
1) Think of a clan you want to join
2) In this bar:
3) Then select 'Create Pride' if you want to make your own Pride (NOTE: 30,000 Gold is needed to create your own Pride/Clan)
If you want to join a pride, select 'Join Pride' and you should come up with this:
Type in the name of the Clan you want to join and press 'Search'
4) Apply for the clan if you wish to join it.
5) Once the master of the pride has accepted you, then only you are now officially considered as a member of their clan.
Hope this helps!