As much as I love Oppenheim's "Slap IT" have read through it many times and still go back to it
if you are a total newbie you might want to start off with Marc Ensign's Slappin': Study of Slap Technique
Short book - good price -starts of a little easier with simple flowing grooves, both in TAB and standard notation. A little more explanatory text written in a friendly style. I see it now comes with a DVD included as well.
Also another good book to go along with these is Chris Matheos Percussive Slap Bass
Another short, well priced book. This is a really fun technique to learn and is great for laying down pulsing backup grooves. I would learn out of this before "Slap IT!", but it dovetails really well into "Slap IT!". Of course, IMHO, YMMV, etc
Also listen to some Brothers Johnson. Louis was one of the pioneer masters! Check YouTube!
"Get the Funk Out of My Face"
"Welcome to the Club"
"Strawberry Letter #23"
"I'll Be Good to You"