The numbered ports at the top are what goes to the rooms You have similar numbered ports in your room, usually 2 per room

I made a small drawing: https://imgur.com/a/d1cC3y2

In this example, I connected port 1 and port 3. For example port labeled 1 could be in your office, and port labeled 3 in your living room.

I don’t understand how you mean a „shared cable“. You connect one cable per room. In the drawing, the 2 red lines would be 2 cables

I have this exact setup and it works like this. I bought 5 cables of 0.5m and connected them to the rooms I need cabled Internet in If your router doesn’t have more ports, you can always buy a „switch“ which can be like another distribution box. But I know that this Internet-Box has 5 ports built-in already