also, would I have to use interrupts to make the GPS tell the car to go from point "a" to "b" and have the car avoid obstacles along the way?
Do you understand what interrupts are? A ringing phone is an interrupt. It occurs at random times, needs pretty much immediate attention, and is externally caused. Which of those attributes applies to you (not the the GPS) telling the car to go from point a to point b? How will you define point b? All the the GPS does is tell the car where it currently is. It still needs to figure out where point b is in relationship to where it is now, and make the appropriate turn(s) to move in the direction of point b, until "here" is point b.