Finding good information online is... challenging. I compiled a short list of some favorite resources on BDSM/kink/leather sexuality:
Bound to be Free, by Charles Moser and JJ Madeson. It's a deep dive into the machinations of the lifestyle, not just the choreography (so to speak).
Thinking Kink, by Catherine Scott. The subtitle says it all: "The Collision of BDSM, Feminism and Popular Culture."
The Ultimate Guide to Kin: BDSM, Role Play and the Erotic Edge, by Tristan Taormino. Yes, a step-by-step procedural manual but so much more.
Sexual Outsiders, by David M. Ortmann and Richard A. Sprott. A great book to mentor someone through experiences in the community. David is a founder and Richard an Executive Director of CARAS (Community-Academic Consortius for Research on Alternative Sexualities).