There are threads meant to give newcomers a basic knowledge of the URPG.
This would be the one you would want to read first - the 'Getting Started' one.
URPG Rules, obviously helpful.
The Starter Requests thread where you can obviously request your starter in the URPG and begin your URPG experience.
After signing up, you can go into individual stickied threads in other sections to help you get a more exact understanding of specific sections of URPG depending on what interests you. Battles are a staple of URPG (and Pokemon in general, really), but differ from "normal battling" in multiple ways that make URPG much more exciting imo. Stories are a cool way to get new Pokemon unobtainable through the Pokemart without having to rely on a bit of luck in the National Park, and are for you if you want to/enjoy writing stories. Park is another method of obtaining Pokemon, and you can role-play for new Pokemon there, though it differs from 'standard' role-playing in some ways. Finally, there are Contests which are essentially dead, but very cool imo. Like with all things, you will get adjusted, for lack of a better word, to the URPG over time.
URPG is also on the Bulbagarden Forums, though it originated here. However, it's much more active over there. With that said, most URPG members do have accounts on both forums for convenience. It's just for some random reasons everyone likes to post over there.
Also, all the threads I linked earlier? They were in this board. Stickied. I'm just saying, maybe it'd be cool if you at least looked at the titles of the stickied threads in a board which you make a thread in saying "Help" and proceed to ask "what is this" in. Especially when one of those threads are titled "Getting Started: Read First". :|