Before posting a question, please check our Frequently Asked Questions page as well as previous threads here. Odds are you aren't the first to ask, and you may find the answer without having to post!
The easiest way to figure out this site is just to ask staff or someone with experience.
To role play, find a thread that interests you And send messages. There are tons; going from interest checks where people can advertise their role play or find partners, groups where everyone gets together to role play, one on one's where you role play with one person, quests where you vote and a game master types it out (those are the best), and other forums that are floating about.