how to work with lowpower node using the sample light switch.

i am using nrf52840dk i have flashed the code for light switch lpn sample in 1 dk and 2nd dk with light sample.

i need to get help with the lpn node how it is acting as lpn node. its saying pressing 

button 4 will be used to temporarily enable Node ID advertisement on the LPN device.   how its working based on the given readme file for lpn node in light switch sample. please help me out on this. Also how friend node is made using the this.
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