An ignition is the firing up of something, usually an engine. Without ignition, your vehicle isn't going anywhere.
You know how igniting is setting something on fire? That should help you remember that ignition means something is catching fire, like the gadget that ignites the fuel in an internal-combustion engine. Turning the key in a car causes ignition: now the car has started. If the car's battery is dead or there's no gas, ignition isn't possible, and the car won't start. To remember what ignition is, just say the catchphrase of the Human Torch: "Flame on!"