The website has good documentation if you're already a programmer. There's a book called HtDP for beginners that the Racket community recommends. http://www.htdp.org/
If you feel like getting some abstract CS and software engineering experience, try out: http://mitpress.mit.edu/sicp/
It's somewhat advanced stuff, but if you feel like it, it's definitely a lot of experience and fun. Just remember you don't have to rush. Take small doses everyday, and within time you'll never regret it.
It might be fun to write your own. The grammar is as simple as it gets, and there are probably less than 10 "special" primitives. In any modern scripting language you could make something that implements eval, lambda, cond, define, etc. in under 50 lines, then implement R4RS in that.