To become a founder of a MC, you have to upgrade your clubhouse to level 4. Afterwards, you can build the annex “church” on the right of your clubhouse. With a church you can now become a member of an MC.
Open up the MC-menu by clicking on the MC-button on the left. To become a MC member you have to apply for membership first. Send your application via the profile of your chosen MC. You can find MCs by searching for them via the MC search, or simply by clicking on scores in the rankings and find them this way. If you wish, you can also apply for membership at several MCs at once. After that, you need to wait for your application to be either accepted or declined. Some MCs do not have an apply button as they aren't accepting new members.
You can establish your own MC by clicking on the pencil button at the bottom of the screen after you have clicked on the MC icon on the left of your screen.