POMEN GTR is right..... some use a smaller switch hidden from view to isolate the ignition switch power and connections, so thief cannot start the car from the ignition switch connector. Thats pretty simple.
The photo shows a different switch, which is used to isolate the battery power from the car, and it needs a relay to do this. A pretty high amperage rating relay. And wiring must be such that in any occasion the power or contact to the switch is lost (accident dashboard tercabut), the relay will open automatically isolating the battery to the whole car. If its wired wrongly, any disastor, or wire putus, the battery will maintain connection to onboard systems deeming it pretty useless......
Hope the above clarifies..... happy DIY-ing.....