Cramming rules
In reply to Dark Legate (msg # 1):
That's a lot of things to answer in one thread, but let me put you at ease at least on that first point.
All of the games that take place here... take place here. That is, on the site, according to the rules. The odd game here or there uses another service, like roll20, to augment their game with maps and such, but for the most part, RPoL is self-contained.
Granted, most tabletop games aren't really designed to be played online, but it's doable, and we make it work.
As for your other points, I can't answer all of those questions in any kind of succinct manner, but here's a couple pieces of advice and general learnin'.
Rules already in editions: There are a whole lot of RPGs out there, from giants like that D&D you mentioned to little bitty one-off games designed by some dude over a weekend. Most of the bigger games, and a lot of the smaller ones, have multiple editions of the rules that have evolved over time. Sometimes, these editions represent little more than rules tweaks, where in others it's pretty much an entirely different game. Dungeons and Dragons, for instance, takes big leaps and bounds between editions. Assuming you're playing the newest edition, 5th, you wouldn't even know that 3rd or 4th edition were the same game if it didn't have Dungeons and Dragons on the front of the book.
General Gist: We play games. Mostly roleplaying games, though there are an odd few non-RPG games out there, including a Magic: The Gathering game floating around somewhere. The style of play is "play-by-post", wherein, in the simplest terms, the players post to threads to announce their actions.
How to create a story: That's a good question. And one even a lot of very experienced players have trouble with. I know of players with literal decades of experience, and they still can't take the GM seat. But overall, I think that the best way to learn is to try, and to muddle through to the best of your ability. If you care enough, and you actually enjoy GMing, you'll figure it out.
How to cooperate with a GM: Communicate. Every GM and every player has different expectations for every game. The only way to reconcile those expectations is through communication. Bug the hell out of your GMs. Talk to them. Ask questions. Listen to the answers. Now, this doesn't mean that you have to ask permission in triplicate for every action you take in a game, but it'll help you get a good sense of how to get on in a game.
How the posting system works: I'd suggest looking through the articles in the Help section up on the top right. Really, this is too general a question to be able to answer without taking up tons of wordcount.