Vi is built on top of an older command line oriented editor called ex.
(Ex and Vi are actually different interfaces to the same program.)
One-line ex commands are accessable from vi by typeing : followed by
the command.
:w
write the file out
:q
exit (if you don't need to save)
:wq
save and exit
:set
set options
all
list all settings
ai
autoindent
noai
no autoindent
sw=4
shift width -- used with autoindent and the shift operators < >