Caching pages

Hey,

i found this url to cache pages
http://scottstuff.net/blog/articles/2005/09/28/rails-caching-presentation

so this should fix the problem like
products/show/1
products/show/2
products/show/3
=> 3 diff caches

then i need to use caches_action_with_params :show, :id

But what is caches_action_with_params ?? Where is that function defined?
And how can u make the cache invalid, if i change the object (like
products/update/1)

Thx
N.