Mopar Performance Distributor adjustable advance?

I have the paperwork with my adjustment kit but I am not understanding it properly.
When people say I have 20 initial what exactly does that mean and how is that obtained? Is it already built in the distributor??
I thought initially I was doing it with the sticks. EX. If i adjusted the gap with 18 stick I was thinking I then had 18 degrees initial but what I think you guys are saying is 18 + the 12 degrees I see at idle means my distributor has 30 degrees mechanical so if so exactly what is that doing for me??
How would I get the engine to have say 20 degrees at idle to help with my 245 @ .050 545 lift cam's idle characteristics??
TY Ron