No matter how much of an expert DIY-er you are, you will still need some solid reference materials. If you are a tradesman, a good text may be even more valuable. When it comes to tools, there is a lot to know and you will need at least one good source of thorough reference material. Tools and Their Uses by the U.S. Bureau of Naval Personnel is the kind of businesslike and authoritative source that no handyman or DIY hobbyist should ever be without.
Anyone just starting out in the world of working with tools (including youngsters considering a career in construction) and building things should read a copy. While obviously a book for personnel in the U.S. Navy, all types of workers can find something valuable in it.