While many people think that there is only one type of yoga practice, there are actually quite a few. Some of these include Hatha yoga, Vinyasa yoga, Ashtanga yoga, and Bikram yoga. Each is unique in how they are practiced, though many teachers integrate the techniques of each into classes.
Hatha yoga is the general type of yoga done at a slow pace. If you are a beginner, this is a good place to start. Vinyasa yoga uses poses called sun salutations that are used in conjunction with breathing.
Ashtanga yoga is a little more physical in that is uses coordinated patterns of repeating poses that are done in continual movement. Bikram yoga is also called hot yoga because it is performed in a very warm room; this stimulates sweating to cleanse the body and also helps to loosen tense muscles.