Great question! Subaru Foresters are designed to take 87 octane (regular) unleaded fuel.
If you’re unsure, check the owner’s manual to find the manufacturer’s recommendations. Most fuels are ethanol blends (usually limited to 10%). Your manual should indicate whether ethanol blends are acceptable to your vehicle.
Some vehicles need special fuel. For instance, if it has a turbo engine, your parents’ Forester may need premium fuel which has a higher octane rating. If your parents didn’t warn you explicitly about fuel, then you can probably assume it takes unleaded.
The fuel door release button is near the floor on the driver’s side. On the right side of the vehicle, you’ll find the fuel door.