You can either download it as a gem,
or if you have the gem system installed :
gem install rools
and use it from within your ruby code
require "rubygems"
require "rools"
#...
If you want it fresh from the source, check out the source by running
svn checkout svn://rubyforge.org/var/svn/rools
and then run
rake gem
to build the latest gem with the latest source.
You can run the unit tests with
rake test
(more about unit tests in the devdoc)