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.

http://grabcad.com/questions/tutorial-solidworks-mold-tools

Parting line is the witness line formed on the component at the intersection of the core & cavity parts of the component. When the component includes undercuts then the witness line around the split is also called parting line.