When you have your fuel, glow plug igniter and all you need for nitro, you will have the wand attached to your drill and insert it into the part I showed you.
There is a one way bearing in there so when it fires it basically won't let the wand spin the wrong direction.
It's what spins the engine so it will start.
That part I showed you is the back plate. It eliminates the starter rope.
I installed one on my Tornado S30 because I hate the recoil rope starter.
I use this...