There might be an inertial fuel shutoff switch, sometimes called a crash sensor, designed to shut off the fuel pump in a collision. This is usually located under the vehicle, near the fuel tank, and is not intended for regular use. You'd only really find this in the case of an accident investigation or repair.
If you need to shut off the fuel supply for some reason (e.g., maintenance, repair), you will need to disconnect the fuel pump's power supply, or perhaps the fuel pump relay depending on the exact configuration. This requires working under the vehicle and disconnecting electrical connectors – it's not a simple task and requires mechanical knowledge.
Caution: Working with fuel systems is dangerous. Fuel is flammable and improper handling can result in injury or fire. If you are not comfortable working on your vehicle, it is best to take it to a qualified mechanic.
