When you're driving, to "pull over" means to stop your car on the side of the road. You might have to "pull over" when a police car stops you, when you have engine trouble, or when you need to look at a map. Here's an example:

When there's an ambulance or fire truck approaching, you're supposed to pull over to the side of the road and let them pass.

You can use "pull over" by itself like in this example. Or you can use it with an object like this:

You're supposed to pull your vehicle over to the side of the road.