Hi there and welcome. A couple things to make your day easier. Please make sure to read the
New to PBP thread, this SHOULD answer several questions about how games are run here.
The way you get into games is by applying to them. You can do so in the
Games and Ads forum. There are several different editions of D&D being played on this site. 3.5, 5E and Pathfinder (a D&D clone) are most popular. 5E is an easier ruleset. The
Adventurer's League Games are always looking for players.
Also check out the
Game Planning forum. This is where people will post ideas for games to see if there is interest. Sometimes, you will find a group of new people who don't know how to play a certain system there, and a GM will step in and agree to run for them. Or a GM will post a game specifically for beginners.
As for how to play, I guess the first thing you will need to decide is
play what? There are a number of systems out there, in several different genres. Some of them have free or inexpensive rulesets you can find online so you can read about them and figure out what you want to play. Find a game your interested in, and you will find a group of people who can help you along to building a character.
Please feel free to ask questions. We are, for the most part, a friendly bunch.