Sales and Purchase od Stock – process

Hi students,

During my career (outside audit) I have never had an opportunity to work closely with Purchase and Sale of stock and stock handeling and thus it makes IC questions really hard for me..
My questions is, do you have any material where this process is described, ideally also with reason? (eg. why 3 part, 4 pard GRN,GDP, whou should notify who… etc)

Thank you.
Pavol