Online help

On some machines (e.g., those running new versions of Linux) there is online documentation for LaTeX, in Info form. Note however that this is not necessarily the most recent information.
You can access it by:

either typing in a shell info latex,
or using Emacs.

To use Emacs, do C-h i (this takes you into Info), then m (which offers the menu selections) followed by latex (at this stage you can already use the completion mechanism of Emacs), and finally RETURN.
Details about the use of Info are given in the Emacs section, under Info.

You can find here the HTML version of the Info LaTeX pages (version 1.6, from April 1996).