Please note, as soon as either the original lower front plate or a Mk4 faceplate is removed from the NTE5C master socket any extension wiring connected to the NTE5C backplate (the part with the "test socket" is also disconnected!
The connections on the MK4/NTE5C are cam lock connectors & do not require a tool. Firstly connect the incoming line connections to the A & B terminals on the REAR of the NTE5C socket (DO NOT connect to the A & B Connections on the MK4!). On some sockets this connector is RED, on later versions it is CLEAR :-

Lift up the cam lock lever, push the wires all the way into the connector and firmly push the lever back into position. If you do not have extensions for broadband or telephones then that completes the installation!
If you have extensions for telephones these connect to the terminals marked 2, 3 & 5 on the NTE5C part. On some sockets this connector is BLUE, on later versions it is CLEAR. To access these connections REMOVE the VDSL MK4 part from the NTE5C- push in the side tabs and pull the MK4 away from the NTE5C :-

Again insert the wires into the connector and firmly close it shut.
If you require an extension for broadband (extension kits available here) , ie, your modem or router will NOT be plugging into the master socket you can wire a broadband ONLY- NO TELEPHONES * - extension to the MK4. Again, remove the MK4 from the NTE5C, on the rear of the MK4 you will see another connector block :-
* A telephone AND broadband modem can connect to an extension wired to these terminals if the socket is filtered, eg, this socket.
These connections are also marked A & B but should not be confused with the line in connections that are marked the same but are on the NTE5C part! On some sockets this connector is RED but on later versions it is CLEAR. Wire your broadband only extension to this connector block. Which connections you use will depend on what socket is being used, if a standard BT socket this would normally be terminals 2 & 5. If an RJ11 euro module terminals 3 & 4 & if a CAT5 or CAT6 mudule the blue/white white/blue terminals (sometimes numbered 4 & 5!).