rails 3 : How to create a path?

I need an explanation about how create new path on rails 3. I want this link for example

link_to "eat chocolate", eat_chocolate_user_path(user)

be equals to

link_to "eat chocolate", :controller => 'user', :action=>'eat_chocolate', :id=> user

I read many guides about it, including routing of railsguide. But i still do not know how it exactly work.