As a beginner, I really liked Bicycling magazines repair manual. Twenty bucks. I could read through any proceedure I was ging to do, have the book open while I dld it and double check when I was done. I printed out some articles from the net on rear derailler adjusting. Between the three things, I finally learned how to do it right. Net articles and the book are useful.
If you decide to buy a book, Read through a few proceedures at the bookstore. Pick the one that has your equipment in it and that you find easy to understand. bk