What it consists of
- Sockets in rooms and offices.
- Cables run inside walls or in trunking.
- A patch panel in the cabinet, where every cable ends at a numbered position.
- A switch and short patch cables.
Which cable
For a new house I recommend at least Cat6, and Cat6A for 10 Gb/s over longer runs. A cable is pulled once, while devices change often. It pays to put in more sockets than seem necessary and to think about spots for Wi-Fi access points and cameras.
Documentation
Each socket should have a label matching its position on the patch panel. Then, years later, nobody has to guess which cable goes where.