This inertia switch is typically located in the passenger compartment, usually under the dash, near the passenger's side kick panel. It's a small, usually red, switch that will cut the power to the fuel pump if it senses a sudden deceleration (like in a collision). If the switch is tripped, it will need to be reset by pressing the button to re-establish power to the pump.
There's no factory-installed, easily accessible switch meant for manually cutting the fuel pump power for other purposes. Adding one would require professional installation and wiring.