Welcome! Some things that come to mind that Toothpick didn't mention is in regards to applying for Roleplays. Most RPs on the site have that "apply" tag next to them, which means they are accepting character sheet submissions. Generally you don't want to post your character into the "Character Tab" until it's been approved by that RP's GM, although there are exceptions. It's always a good idea to ask questions in the "OOC Tab" of each RP! The Tab system seems to be something unique to this forum versus other RP forums, so may want to keep it in mind. Otherwise, it's pretty similar to table top just less dice involved (and less first/second person narration).

Generally people are pretty friendly and willing to help out if you have any questions. Enjoy your stay!