I wrote two blog posts about custom properties. One to teach you the basics, like what does \$PRPSHEET mean and how to get started with the property tab builder:

How to work with custom properties (and cut lists) | CAD Booster 

I was going to include a complete list of all available variables because SolidWorks does not publish that list. The table became so large that I created a separate post for that:

All available variables for custom properties (and cut lists) 

Are there variables that I am missing? I'd love to make that table even larger, or dare I even say complete