acts_as_tree questions/problems

I'm trying to get acts_as_tree to work in a project running Rails 2.1.0. The plugin's documentation is extremely scarse and after some trying and Googling for more info, I gave up.

So, the question is: can anybody give a short but (for a Rails newbie) clear explanation or example of what needs to go where in which order, when setting up an app with this plugin based on the example's in the readme or (better) as given in Agile Web Development with Rails (pp. 354-356).

Probably the example code in the readme is enough for the more experienced ROR coder, but not to me. I also read the pages on "Acts_as_tree" in the "Agile web development with Rails" volume, but without any result.