Malc,
I'm setting up my first one but I'll elaborate on RCIGN1.
You'll find samples of kill switches at Tower.
Mine is a set of switches wire together. one is a slide switch mount thru the side of fuselage; the second one is a Normally open momentary switch activated by a lever.
These get installed away from all sevos and radio gear.
A non-metallic pushrod from a dedicated servo and channel on TX is set-up to "push" on the switch lever when you activated it via your TX.

Normally, when the two wires are connected together (coming off the engine) you are "shorting out" the ignition killing the spark to the plug.

This should answer your basic ? I'm sure if this info is incorrect someone will correct and elaborate.