Saving Blocks

Hi, firstly sorry for this post, it comes from an AutoCAD newbie and I think
would be pretty elementary to experienced users.
I have designed several items in drawings in which I have also created a number
of Blocks for insertion, my question relates to
where AutoCAD saves those blocks and under what name/extension.
Are the Blocks that are created with a drawing saved as part of each drawing
respectively, or are they saved elsewhere? If they
are saved with each drawing can I change things (settings or otherwise) to allow
me to use these Blocks in other drawings or do I
have to copy and save each Block in each drawing?
Thank you for your help, all assistance is greatly appreciated.
Cheers
Mike the Kiwi