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?