Before we can start using mu4e, we need to tell
emacs to load it. So,
add to your ~/.emacs (or its moral equivalent, such as
~/.emacs.d/init.el) something like:
emacs complains that it cannot find mu4e, check your
load-path and make sure that mu4e’s installation directory is part of it.
If not, you can add it:
(add-to-list 'load-path MU4E-PATH)
with MU4E-PATH replaced with the actual path.