If you are using a neoPlug just to boost the signal between a wireless thermostat and a receiver or a wiring centre.
To install it, just insert the neoPlug into mains between the thermostat and the receiver and turn the power on, it will start to repeat. You do not need to do anything else. It will automatically pick up any wireless radio signal from our neoAir, Slimline RF or Touch RF range and relay it back to the receiver/wiring centre.
The button is only used if you have a neoHub and you are looking to add it to the neoApp. In addition it does not matter if the light is red or green.
For information, the reason why there are red and green lights is because, if you add it to a neoHub, you can turn the neoPlug into a Smart Plug. Meaning if you have something plugged into it, you can turn the device on (green light) or off (red light) via the App. If the light blinks, it means it is not connected to a neoHub.