These exercises are meant to be used alongside vimtutor, in order to
get more practice with the commands taught. Open vimtutor in one instance
of Vim, and vim_ex.txt in another instance. Most lessons in vimtutor
will have an equivalent exercise in vim_ex.txt, except for those where
it doesn't really make sense to have a separate exercise.
To start vimtutor, run vimtutor from a terminal. To open the
vim_ex.txt file in Vim, cd to the directory containing the file and
run vim vim_ext.txt.