Thelema has no single church. Two bodies carry most of the tradition, and they do different work.
A.'.A.'., founded in 1907, teaches individuals. There are no congregational meetings. A member knows only the person who admitted them and those they admit in turn, and progress runs up a ladder of grades borrowed in structure from the Golden Dawn and mapped onto the Kabbalistic Tree of Life, from Probationer through the Adept grades to those above the Abyss. Each grade carries a syllabus and a requirement to keep a magical record.
Ordo Templi Orientis is a collective initiatory order with lodges, dues, degrees and officers. It is older than Thelema and Masonic in shape, and Crowley reworked its degrees around the Book of the Law and around a sexual teaching held as its central secret. Its public ceremony is the Gnostic Mass, Liber XV, a eucharistic rite with priest, priestess, deacon and two children, in which the consecrated elements are consumed by the communicant rather than reserved to a clergy, and which functions as the movement's most visible congregational service.
Crowley spelled the discipline magick with a terminal k, partly to separate it from stage conjuring, and defined it as the science and art of causing change to occur in conformity with will, a definition broad enough to cover any deliberate act. Practice includes Liber Resh, four brief solar adorations at dawn, noon, sunset and midnight; banishing rituals inherited from the Golden Dawn; a calendar of holy days built around the equinox in March and the three days of the writing of the Book in April; and heavy use of qabalistic number, with 93, the value of both Thelema and Agape, will and love, serving as a greeting.
Crowley's writings remain the working corpus: Magick in Theory and Practice, the Book of Thoth with its tarot, the Holy Books of Thelema, and the Confessions. Smaller independent Thelemic groups exist alongside the two orders, and disputes over lineage, authority and copyright have been a recurring feature since his death.