Skip the books and take an NRA reloading course ("Basic metallic cartridge reloading"):
https://www.nrainstructors.org/search.aspxThis is what I did 3 years ago -- and it's how I got into cowboy action shooting. I wanted to learn how to load black powder ammunition, and one of the students recommended that I go to a SASS shoot and meet some black powder shooters. He even ended up selling me my first cowboy rig
The course was hands-on and got me going instantly. You learn the basics in a safe setting with a knowledgeable instructor. You put your hands on the equipment and learn the basic techniques under supervision. The instructor will also give you guidance on how to get your own reloading gear setup.
If you really want a book, buy a manufacturer reloading manual. Most people that load ammo own several. I have Lyman, Speer, Nosler and Hornady.