The definitive guide to LaTeX is LaTeX: A Document Preparation System, 2nd Edition, by Leslie Lamport, published by Addison-Wesley, 1994, ISBN: 0-201-52983-1. An excellent supplemental guide is The LaTeX Companion, by Michel Goossens, Frank Mittelbach, and Alexander Samarin, also published by Addison-Wesley, 1994, ISBN: 0-201-54199-8.
Freely available tutorials include the following. They are a little dated, but still relevant. If you use the LaTeX source, remember to run LaTeX twice before dvips to generate the PostScript. Thus all cross-references (e.g. figure numbers) will be correct.