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