How does the points and race earnings work in NASCAR?

For example the past weekend at Infineon, Dale JR made $125,808 and finished 13th in the race where as Kyle Busch only made $105,350
For finishing 8th. I may be answering my own question but is based on driver contracts with a percentage of the purse total. Like say if a driver gets paid $75,000.00 per race regardless of where he finishes and then an additional 10% of the race winnings and so on.

Yes, each position pays a certain ammt of the purse. Then, from there drivers get more monies depending on their sponorship deals (the more little stickers on their car, the more money), their personal team contract and any bonus awards that may be on the line.