The ignition switch is situated inside the vehicle, usually on the steering column or dashboard. It can be key-activated with a barrel lock mechanism, but some vehicles use a keyless ignition system that is operated by pressing a button on a key fob. 

The ignition switch activates all of the main electrical systems in the vehicle including the radio, lights and windows. It ignites the fuel and air combination of the combustion engine and allows the starter motor to operate. The battery is also engaged once the ignition switch is turned. 

If the ignition switch is not working, you will not be able to start the vehicle without bypassing the ignition switch, as it locks when not in use. To bypass the ignition switch, the wiring will have to be disconnected and manipulated directly, behind a panel in the steering column - otherwise known as hotwiring.

It is also possible that the switch will operate, but will not turn when the key is inserted. This could be caused by a worn key or the steering column binding. In the case of the latter, this is sometimes solved by wiggling the steering wheel back and forth.