Although yoga has been defined and practiced in a variety of ways over the centuries, the modern version can best be understood as a practice comprised of three main components: yoga postures (asanas), breathing techniques (pranayamas) and meditation. The main goal of yoga is to bring the mind, body and breath into perfect harmony.
If you are an absolute beginner, start with a true beginner class wherein you will learn the basic poses from scratch. Many studios will state that classes are open to “all levels,” although that doesn’t necessarily mean that they will stop to teach you the poses if you don’t already know them. If in doubt, ask one of the instructors.