What kind of cable do you use to connect a computer to a network?

You would use a network cable to connect a computer to a network. The type of cable and its electrical, possibly optical, and mechanical attributes depend on the network's pysical layer.

Networks use a variety of fiber optic cables, coaxial cables, single twisted-pairs, double and quadruple twisted-pair cables. Other forms exist, including those not requireing a dedicated cable (such as some devices designed for networking over power line), or not requireing a cable at all (such as devices designed for networking over radio frequency connections).