Binah is sephirah number 3 and known as Understanding.  Binah is the bright fertile Mother of Creation and the dark sterile Mother of the Underworld.  On the Tree of Life Binah is situated at the top of the black pillar of Form.  Without form, energy cannot manifest.  Binah represents the Womb of Creation and Mother of Form.

There is a Binah workbook available in pdf and paperback format.  Read the reviews to help you to decide if these workbooks may be of use to you.