What is a parting line in mold design in SW?
This is a theoretical line on the part that is used to create the parting surfaces. See previous answer. These are usually edges of the part.
I think someone has put up a tutorial? If not if I get a chance I will. However if you go to SolidWorks Tutorials they already have a tutorial on Mold which will lead you through the steps.
It helps to have an understanding of how molds are made in the first place.