Stance is really just how low your car is, and how your wheels are tucked. Most kids running around with "stanced" cars just slap on shitty coilovers, max them out so they have horrible negative camber, and call it a day. This will wreck your suspension, tires, and rims in the long run. What you SHOULD do:
Invest in a good suspension package. I'd suggest fully adjustable coil overs (Function and Form, Progress CS-II's etc.), and a camber kit as well. People will argue that you don't need a camber kit, but if you're slamming your car, you're going to want one regardless.
Offset plays a huge role in "stance" as well. Offset, put in layman's terms, is how wide your wheels sit from the fender/wheel well of your car. A negative offset gives wheels a "deep dish" look, a positive offset will place them a bit further out from the fender/wheel well. I'd drop by a reputable shop that knows their wheel s**t and talk to someone about what you want.
Tires are important as well. There's a "stretch" trend going on right now, where people will take super thin tires and stretch them on rims they normally wouldn't quite fit on, to give the car a lower ride height. I wouldn't ever do this, and I don't recommend ANYONE to do it, but to each their own.
