If you're embarking on a road trip in a rental car, it's fair to say that you're going to be a little nervous. Driving a car you're not used to can be daunting, and it can take a little while to work out its little quirks and intricacies. But if you're not sure which side you need to fill the car up when you get to a gas station, the car should be able to tell you.
In fact, all you need to do is look at the dashboard and check out the arrow by the gas tank icon. If the arrow is pointing left, you should fill up on the left. If the arrow is on the right, fill up on the right.