Hi Sharyn,
I believe that Thelema is an occultic practice. It’s most famous practitioner was Alleister Crowley, who was and Englishman that lived in the late 19th and early 20th centuries, he styled himself as “the evilest man alive” and his nickname was “the beast.” He pursued enlightenment through occultic practices such as transcendental meditation, contacting spirits, and out of body experiences. He was influenced by some eastern philosophies and some ancient Egyptian mythology. His Thelema teachings were also mixed with heavy drug use and experimentations in “free love.”
To Thelema practitioners their whole creed can be summed up as: “Do what thou shalt will as long as it harms no other living thing, shall be the whole of the law.” This was later picked up by Anton LaVey and his satanic group he formed.
This is a pretty broad outline but I think I got it correct. Maybe others can add more detail and I know the internet has information about Thelema from groups that claim to follow it and a lot of Crowley’s writings are online, but be warned they are obtuse, boring and incredibly hard to follow full of esoteric mumbo-jumbo that makes little to no sense.
ChadS