Can I drive my car with a temporary registration?

I just got a great deal on a used Hyundai Elantra that has low miles and is in great shape. The only problem is that it didn’t come with an owner’s manual. My immediate issue is that I’m at the gas station, and I’m trying to figure out how to open the door to the gas tank. How do you open a gas tank on a Hyundai Elantra?

I read somewhere that the timing chain should be replaced when a car is really old. I haven’t done so before, and I think it’s about time. What is the cost of a timing chain replacement?

I was in the Target parking lot the other day loading up my trunk, and the car that pulled up beside me flung open the door, and it dinged my door. The dent isn’t huge, but it’s more than noticeable. I didn’t say anything then, but now I have a $500 car repair bill. What should I do if this happens again?