How can I go to a Clan?

you post on the clans application page.

these usaully include your:
Name
Belt
How long you have been playing
why you want to join.

but note that clans usaully have a Belt limit, (black belts and up for example). you should also be ready to commit yourself to a clan before posting an app. you have to be actice or they might kick you out

Check this page.
If you want to get in a clan easily, I'd suggest you build up a good reputation and some skills.