Here are the best books to learn . (See this list in Best Books!.)
More than enough to get you started. Included in most distributions.
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.
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.