Jnana yoga is focused on finding liberation by using thought to transcend thought. Tantra yoga, perhaps the most misunderstood form of all, is based upon the principle of consciously embracing the whole of life in order to transcend it and thus unite with Deity. There are many schools of each of these disciplines, just as there are many branches of churches which can be called Christian. The most popular forms of hatha yoga in the United States today are Iyengar and Astanga, which are both rather vigorous. Additionally, there is a move by many teachers toward an eclecticism that combines two or more approaches.
Yoga is one of the orthodox philosophies of India.
While it is not a religion, it is theistic, i.e., it teaches the existence of a Supreme Intelligence or Being. However, to practice the techniques of yoga successfully you do not need to believe in such a being. Because yoga is a spiritual rather than a religious practice, it does not interfere with any religion. In fact, many people find that it enhances their own personal religious beliefs. The best way to learn yoga is to study with a teacher you respect and with whom you feel comfortable.