Pull up to the the pump. Make sure your gas tank is on the same side as the pump.
If paying cash, go to the clerk now and give them the amount you want to pay with. It can be $5, $10, $60 etc. Don't forget to tell them which pump your car is at. If you wish to pay with your debit/credit card, you can do that right at the pump. Slide your credit/debit.. enter your zip code and wait for it to authorize.
After that, open the little door and unscrew the gas cap. If you hear clicking, you are unscrewing it the wrong way. If you do not hear clicking, you are doing it right. It might take a little muscle to unscrew it.
Select the grade of fuel you want. Put the nozzle into the gas tank of your car and lift up on the handle and hold it. You can see how many gallons is being pumped and how much you are being charged. If you pay cash it will stop at the amount you gave the clerk. It will stop at a full tank if you paid credit. If you do not want a full tank just lift up on the nozzle when you want it to stop.
When finished put the nozzle back in the holder and screw the cap on until you hear clicking. Close the gas tank door. If you paid credit hit yes/no for your receipt. If you paid cash you already got a receipt.