This is a tp-link powerline adapter commonly used to connect your computer to the internet we are the power line
You will have one box connected to your router and the other box will in the room situated fat from your router.
They are especially useful when Wi-Fi network don’t go through don’t reach far away rooms
As you probably know the electrical power comes transported on a copper wire and it’s a sinusoidal wave. On this wave the Powerline adapter will superposed your internet signal without damaging any of you electrical Appliance or interfering with them.