Here's a close up of the clamp. It looks to have some form of magnet inside. I'm not clamp meter expert so see Wikipedia for an explanation of how they work!
To pair with the WiFi link you just put the sender into learning mode (press and hold a button) and select an option on the UI of the WiFi link. When paired you get the latest reading from the sender always shown on the WiFi link screen.
You can view the measurements on the web interface or via the handset app (example shown below):