According to their website:
O.T.O. is an Outer Thelemic Order which is dedicated to the high purpose of securing the Liberty of the Individual and his or her advancement in Light, Wisdom, Understanding, Knowledge, and Power through Beauty, Courage, and Wit, on the Foundation of Universal Brotherhood.
Hope that clears everything up.
Originally intimately related to the mystical orders of the Freemasons and the Golden Dawn, the Ordo Templi Orientis seems now to be almost exclusively devoted to the vision and inspiriation of Aleister Crowley. Crowley was the Outer Head of the Ordo Templi Orientis for many years, having been initiated into the order after a curious incident which he relates in his autobiography.
The head of the Order came to visit him one day, and said that it was absolutely urgent that Aleister be initiated into the Order's highest rank, as he was familiar with their most preciously guarded secret ritual. He was totally clueless as to how this might be, until the man turned to Crowley's bookshelf and selected a slim volume, opening it swiftly to a specific page. it turned out that he had written cryptically (and unwittingly) about it in chapter 23 of The Book Of Lies. He does not relate what happened next, but I can imagine the old trickster nodding gravely and feigning perfect knowledge of the 'secret', sensing an opportunity to gain power and respect.
The canonical text of the O.T.O. is Crowley's Liber Al Vel Legis, otherwise known as The Book Of The Law, an inspired work which Crowley claimed was dictated to him by a discarnate being, and in which he declares the Law of the New Aeon: Do What Thou Wilt Shall Be The Whole Of The Law.
The Order is dedicated to the spiritual and personal growth of the individual through the practice of magick and the exercise of will. The Law 'Do what thou wilt...' is often misunderstood, with critics accusing Crowley of encouraging rampant and selfish individualism without compassion or love. In fact, Crowley's idea was that, in a healthy individual, the True Will would never be to harm any other living being, and this is why he laid so much emphasis on healing personal neuroses and character defects before attempting any more advanced magickal techniques.
For anyone interested, according to Robert Anton Wilson, the great secret of the O.T.O. is a sexual magick ritual with its roots in Tantra Yoga.