If you install it from the elpa.gnu.org repository with Emacs' package manager,
you only need to enable the mode, e.g., in your =init.el= file:
#+begin_src emacs-lisp
-(add-to-hook 'after-init-hook 'company-statistics-mode)
+(add-hook 'after-init-hook 'company-statistics-mode)
#+end_src
Alternatively, make sure =company-statistics.el= is in your =load-path=, and add