Hello and welcome to...
Wah, look at all the responses. x____x
Oh, right, ahem! Welcome to Iwaku. I'm Kitti and it's good to meet you.
Since you're new and don't know what to do, you should check out what I have to show ya~
This is where you can sign up for the roleplays found in Modern, Scifi, Fantasy, and sometimes Mature. Generally, they will have you post a character sheet in their thread, a new sheet for each roleplay! You can also start signups for a roleplay of your own here. Iliana already pointed you here, but I figured I'd expand on its purpose a bit!
This is where you can find jump in games, which typically have no sign up thread. You just start posting!
If you have any questions, please feel free to ask.