Basically, its an electronic control module you mount remotely (under helm or dash) that replaces the key switch. All the wires that were on the switch are connected to the control module and a push button with LED light ring fits into the existing key switch hole.
The module has a cut-off switch that disables the push button. You can also wire the original key as the cut off switch if you prefer. I have just a standard toggle switch hidden under the dash that enables the push button start. That way when I leave the boat, I throw the toggle and no one will be able to start it unless they know where the switch is.
The button toggles between OFF, ACC, ON then back to OFF. To start, you push and hold until the engine fires then one push to kill the engine and go back to ACC. In ACC, the ring light pulses (MacBook heartbeat style) and in ON the light is solid.