There are a lot of different places where it's possible to give or receive oral sex -- in the shower, in bed, on the kitchen counter, etc. But one of the most fun and risky ways is in a car while on the road, and it's known as "road head."
The first thing to keep in mind when trying road head is that it's incredibly dangerous. If a man isn't fully focused on the road, he could hit a pothole and lose control of the vehicle, possibly causing an accident and hurting himself or his passenger. Depending on where you live, there may be laws against road head and lewd or indecent behavior in public, which can lead to fines.
If you want to try road head, make sure you're on a deserted road and that no other cars are nearby. It's also important that you use a vehicle with a back seat that can fold or be removed, as it'll make it easier to reach your partner. And don't forget to take your phone out of your pocket, so you can answer calls if needed.
To start, stroke your partner's foreskin up and down, then slowly begin to move closer to the crotch area. Once you're close enough, you can put your hand under his pants and start stroking up and down the shaft. As you stroke, say something soft and seductive to build sexual tension, and when he's hard, take his cock out carefully so that it doesn't get stuck on the zipper of his pants.