This package is distributed with Emacs, so there is no need to install any additional files in order to start using it. Lisp code that uses features from this package should simply include at the beginning:
You may wish to add such a statement to your init file, if you make frequent use of features from this package.
Code that only uses macros from this package can enclose the above in
eval-when-compile. Internally, this library is divided into
several files, see Organization. Your code should only ever load
the main cl-lib file, which will load the others as needed.