When you pull up on this lever, your fuel door will spring open. Then, you can exit your vehicle, pull the fuel door fully open, and unscrew your gas cap by turning it counterclockwise until it comes free from your vehicle. Then, you can fill up your gas tank as normal.
If your fuel door doesn’t open when you pull the lever, it may be frozen shut. If this happens, simply push or tap lightly on the fuel door to dislodge some of the ice. This should free your fuel door.