The LaTeX macros encourage writers to think about the content of their documents, rather than the form. The ideal, very difficult to realize, is to have no formatting commands (like ``switch to italic'' or ``skip 2 picas'') in the document at all; instead, everything is done by specific markup instructions: ``emphasize'', ``start a section''.
The primary source of documentation for LaTeX is the LaTeX manual referenced below, and the local guide in the file local-guide.tex or local.tex or some such somewhere in the directory @TEXINPUTDIR@.