Here are the best books to learn \(\LaTeX\). (See this list in Best Books!)
1. The Not So Short Introduction to LaTeX2e
Tobias Oetiker et al. » The Not So Short Introduction to LaTeX2e (pdf)
More than enough to get you started. Included in most LaTeX distributions.
2. Guide to LaTeX
Helmut Kopka » Guide to LaTeX
Mostly intended for beginners but actually more appropriate for heavy LaTeX users. It covers all the basics and then goes on to more advanced subjects like drawing and advanced customizations. Lots of examples, very good explanations.
George Grätzer » More Math Into LaTeX
Great book with an exceptional introduction for beginners which is even available online: Short Course.
This is about TeX but it’s a great book. Covers from small things to internals of TeX and typography. Definitely worth reading.