The online help is hypertextual in nature; you use the tag
commands ^] and ^T to
follow a reference and to go back to a previous position.
If you have a color display, using the help with syntax coloring
is particularly pleasant and effective.
The hypertext format is unique to vim; however
the doc directory contains a Makefile
and awk scripts
that convert the files into HTML for perusal with a Web browser.
(The html display mode in elvis
works just fine.
)
The point to start from would be help.html,
generated from help.txt, the starting point
for the online help.
Also included, of course, is a UNIX man page for vim.