@Shiva Tseba'oth said
"Liber DCCCXXXVII – The Law of Liberty
Liber II – The Message of Master Therion
Liber CL – De Lege Libellvm
Liber LXXVII – Liber Oz
Liber CCXX – Liber AL vel Legis
That's some good books for a beginning."
Ditto that. De Lege Lebellum is an excellent introductory text. Liber AL is the core and cornerstone of Thelemic literature.
There's a compilation, of reasonable price, called "Portable Darkness." The editor's intro and comments are bullocks, but it's a good beginning reader, and contains both of the above.