What does this instruction in the Bundler setup mean?

I'm trying to setup Bundler with Rails 2.3.10 to make the transition to Rails 3 easier. But I'm not sure what the instruction on this page means. Am I supposed to require all the gems that I'm using in my app? If so, where? Thanks for reading.

From stackoverflow

• Use the Rails 2.3 tutorial http://gembundler.com/rails23.html it's better on your case.

  The setup made all requirement of all gem in your Gemfile. He avoid to do a lot of require ''.