Originally Posted by Jeff Wills

+1. I'll assume you bought a Schwinn Miramar. Just ride it. Don't obsess about the parts. If you ride it enough you'll start to wear stuff out. When you get tired of replacing parts, go to a bike shop and see how what your budget gets you. Subtract about 10%, buy a bike, then spend the difference making the bike right for you.

What newbies (and many experienced cyclists) fail to comprehend is that fitting a bike to your body is at least as important as what equipment is on the bike. At your height and weight you've probably found it tough to find clothes that fit "off the rack". (Me, too- I'm 6-foot-4, 220 lbs.) The same applies to bikes. Yes, you can buy something off the shelf that rolls, shifts, and stops, but there's a vast gulf between that and a bicycle built for you.

For now, though, just ride. Get used to riding that bike, figure out what you like and don't like about it. As your muscles develop and fat burns off, you'll figure out what your next step will be. Happy trails!