Right here, in this very forum, in the play by post section. Browse the thread, find something that's recruiting (aimed at newbies) or ask for a game yourelf, and jump right in.
You can find most of D&D rules (3.5 edition) avaiable legally and for free Here. And you'll need a place to store your character sheet online. Here's a good one.
D&D is based on dice rolling. This forum has a built-in dice roller. Here it explains how to use it.
And of course, you can always PM me if you have any trouble.
WELCOME TO THE FORUM!