What we call yoga here is actually hatha yoga, which describes the physical postures that can produce optimal health. My best suggestion for finding an optimal yoga practice is to find a very good yoga teacher, someone who has extensive training and certification. Some newly popular forms of yoga can be extremely vigorous and may need to be balanced with some of the milder forms. In general, you can practice yoga, and many people do every day for benefit, although with some of the more vigorous forms, it's not optimal to work out hard every day of the week. It's typically better to alternate a hard workout with an easy workout.
Yoga is extremely versatile.
Even sitting and focusing on your breaths is a form of yoga practice. But it's best practiced through a qualified instructor. Yoga Journal is an excellent publication. They have a listing of certified yoga teachers. I'd suggest it for people who want to learn more about yoga.