hello! welcome!

Just join an RP and then follow further instructions to fill out their sheet and give them. In case you wanna start your own, you should first go to the search section of the site, and start a thread there.
Welcome :)

Roleplays are all down under the Roleplay header, sorted by setting (or, as with Dice, Nation Building, Coliseum, and Quests, by type).  There are also 1x1s, which are roleplays of any setting that only have a couple people involved; and Hosted Projects, which are roleplays of any setting/type that are complex enough to need a miniforum of their own.

Above Roleplays you'll see Looking for Players.  This is also referred to as the Interest Check section, because it's where people post ideas or roleplay summaries to recruit new players, or post what sort of roleplay they want to join.  It's divided into Looking for Partners for 1x1s and Looking for Group for larger roleplays.

How to start a new one: I suggest getting an interest check thread first, and then creating your roleplay once you have some players.  That way you know you have someone to play with!  Once you're ready, go into the section in Roleplays that you want your RP to be in, and click Start New Topic.  If you want extra threads (for characters, OOC chat, or whatever you like), go into the subforums of your RP's section and create a new topic there for it.  We recommend having links to those other threads in the first post of your RP, to make it easier on your players.

If you have any other questions, feel free to ask in Site Questions & Information or in Roleplay Discussion & Advice, whichever fits your question better.

Happy roleplaying! ^33^