Hello I don't know if this is the right topic but I was wondering if any one could tell me how to breed my great plains rat snake and my corn snake?

Corn snakes are a type of Rat snake, so you should not have a problem. Many of the variety of corn snakes are easily bred with other types of rat snakes including milk snakes, king snakes, etc.

Have you confirmed the sex of both? If so, and you are sure they are male and female (this is easier said than done... but another topic) then put them together and give them some time.