To which part of the computer are the usb-ports connected?

Answer 1

Well, it's connected in the back of the computer to something like a CD player, only it reads the information on your device you attach to it, like an mp3 player.

Answer 2

Physically? To the motherboard, or a USB adapter card that plugs into the mother board.

Electrically? To the USB controller chip. Usually located in the southbridge controller.

Answer 3

to the MB (Motherboard).

Most stores sell them on a bracket with 2 ports, 4 ports & up. The wires from them will all go to a single or 2 plugs that you hook up to the pins on the motherboard.