Note that vim includes a useful tutorial you can invoke by "vimtutor" on the command line or from within vim with ":help tutor"; for neovim try ":Tutorial".

Nvi has :viusage and :exusage. Vim is not POSIX vi; vim to vi it's what zsh it's to sh. Nvi2 it's closer as it has very few additions on top of vi, but it has Unicode support which can be a lifesaver if you live in Europe or Japan, allowing you to use Nvi everywhere (I do, as it's my post editor under Mutt/Slrn,Tut and so on).