When you're travelling in a car, "stopping to ___" means to stop the car, so that you or the passengers can do something:
I need to stop to pee soon.
Would you mind stopping to get some trash bags at the grocery store on your way home?
Notice that the meaning of "stop to ___" is completely different from "stop ___ing". "Stop ___ing" means that you don't continue doing something:
When are you going to stop smoking?