ignore me plugging ethernet cables into the ports because why not
The first thing you want to know is where each of the cables go. The top black area is just for phone and you don't need to worry about it. The bottom 2 black blocks go to ports around your house. To determine where they go plug your router into one of the wall ports in the house then try plugging your laptop into different ports on the bottom black 2 boxes and repeat for all ports. Write some labels so you know where each port goes - usually a label with a number with the wall socket having a number "1" next to that number you add a sticker to on the black boxes.
You then will need to either put your rotuer in this cabinet with a cable connecting to your fibre box on the "WAN" router port then the LAN ports to spots in your house or else buy a network switch such as this one:
With a switch one connection would go back to the router's LAN port and then the remaining ports would go to the wall sockets you have labelled.
And they snipped the POT's line too. Oh dear.
They could be marked behind the faceplate 1-8 already too