I highly recommend the Vogue Knitting Book. It has never failed to answer my every question! LOL. It isn't very portable, but it is very useful and thorough.
There are of course MANY others worth having-for instance anything by Elizabeth Zimmerman is wonderful. I have her Knitting without Tears and Knitting Workshop (both excellent for beginners!) and also the Knitter's Almanac, and Knitting Around. Both of these are quite enjoyable and worthwhile as well.
I always wonder why my last stitch on cables is so loose too
I don't know the second and 3rd question, but the last one: a selvage stitch is any stitch on the edge of the piece.