Make sure that all of your doors are unlocked when you do this, as you won’t be able to open your car’s fuel door if any of the doors are still locked. This is a safety mechanism put into place to protect your gas tank while your car is unattended.
When you press inward on the fuel door, it should spring open, revealing the vehicle’s gas cap. Unscrew your gas cap by turning it counterclockwise until it comes free from your vehicle. If your gas cap is stuck, try wiggling it slightly to make it straight.