Welcome to RPG! The technology part of this site isn't too difficult... Just make sure that when you post pictures or format text, use the QQcode cheatsheet that is under the post window. So for images, you would write img= and then the url of the image, and put that whole thing in brackets.
As for the do's and don'ts of RPing, that's mostly up to you. The one big rule is NEVER have "intimate interactions" in public threads, as there are many users on the site under the age of eighteen. There's no reason you can't do RPs with mature themes, just make sure that once "things" start to happen, you take it to private conversation.