There are three main cables to choose from when designing a network. Most cables have a central conductor, a wire, surrounded by a plastic jacket. Phone companies most often use this type of wire, but increasingly it has found its way into computer networks.
Copper wires attract other signals just like a radio antenna.
Putting copper wires together means they can interfere with each other. To prevent this interference two copper wires are twisted together, in effect canceling out emitted signals from the other wire and protecting the set from outside noise. Normally, twisted-pair cables are color coded and coated with plastic jackets. Cables can have more than one set of twisted-pair. Because of this telephone and data cable runs can be made at the same time.