(in this example the back of a Fanvil X5U is shown)

USB Port - used with the Fanvil WiFi dongles & USB headsets
(USB port not available on all IP Phone models)

Power Port - used for connecting the power adapter to the phone 

Local Network Port (LAN on some phones)- used for connecting the local network (LAN/Ethernet) cable to the phone

PC Port - The PC port should only be used if there is only 1x ethernet port available during setup of the phone. In this setup the phone will feed the internet to your PC (AKA Bridging)

See Also -Using an IP Phone to bridge between the local network and your PC

Headset Port - used for connecting a headset using a EHS cable (sold separately)

Handset Receiver Port - used for connecting the IP Phone handset