There are several possible reasons why you might only get a couple of channels if you aren't using cable or satellite:
1. Distance... If you're too far away from most stations, then you might only pick up one or two (if you live in or near a city, this is probably not your problem).
2. Antenna type... You may not be using the best type of antenna for the stations in your area (an HD antenna won't necessarily work better than a regular old one; what is more important is VHF vs. UHF, and antenna orientation, and that depends on your area). Go to www.antennaweb.org to get recommendations based on your address.
3. TV tuner type... If you have an old TV that does not have a digital tuner, then it won't pick up most channels, since almost all stations switched over to digital nearly a year ago. If that's the case, getting a digital converter box, or a new TV, will fix this problem.