Do what thou wilt shall be the whole of the Law.
Many Thelemites are also practitioners of magick, which was defined by Aleister Crowley as "the Science and Art of causing Change to occur in conformity with Will". By this definition, magick is especially appropriate for Thelemites, given the emphasis of Thelema upon the individual discovery and following of the True Will. Spelling the word with a "k" at the end serves to distinguish the spiritual discipline of magick from sleight-of-hand tricks and stage magic.
A practitioner of magick performs rituals, either alone or as part of a group, designed to accomplish a given purpose. A ritual is a pre-determined series of actions which might include gestures, chants, recitation of invocatory lines, visualizations, meditation, etc. Rituals are most often performed in a designated setting, which may be a sacred grove or other outdoor location, or an indoor space equipped as a temple. Candles, incense, and magical implements such as the wand, cup, dagger, and pantacle may be used, according to the requirements of the particular ritual. All of these elements combine to imprint the desired change in the consciousness of the magician.
For the definitive explanation of magick, refer to Aleister Crowley's Introduction to Magick. Crowley wrote and published a great deal about Magick, including many rituals, and much of it is in this indispensible book.
Love is the law, love under will.