reading API ?

How to read the Rails / Ruby Api ?

This question comes on my mind when I look at ActiveRecord::Base documentation. I am looking for all methods that are available on ActiveRecord::Base, but i couldnt know.

For example belongs_to, has_many .. is actually belongs to ActivRecord::Association...and Association is part of ActiveRecord::Base (I knew it from the books .) ... but how i know about all methods (that belong to parrent classes as well) that is available by reading Rails API ?

thank you