In reply to AlisonSmiles:
Rock climbing: Essential skills and techniques by Libby Peter is an excellent resource for all of the basics and beyond. It has very good descriptions and diagrams of most situations you will encounter with anchors in and out of reach etc
Climbing Anchors by John Long is good if you like full on nut on rock action (with graphic pictures to boot) and descriptions of virtually every variety of anchor you will ever and never be likely to need.
For what you've specifically asked for, I'd go for the Libby Peter book.