Answer by romainl for What is the difference between s, c and r commands in vi/vim?

:help c
:help s
:help r

Easy.

Instead of wasting your time on that book, learn how to use Vim's awesome internal documentation:

:h s
:h :command
:h 'option'
:h function()
:h ctrl-x
:h i_ctrl-x
:h subject
:h foo<Tab>
:helpgrep foo