While electricity has been in common use for over 100 years now, the systems that were used to deliver it to homes and other buildings as a power source have changed a lot over the years. Electrical wiring, or the use of insulated conductors to carry electricity, has also undergone a great number of changes, just in the past half dozen decades. Modern electrical wires though are made of copper, and are insulated with sheathes of plastic which are color coded for the ease of electricians. White, black, and green are three of the most common insulation colors.
Without involving devices in the transit of electricity, or those used in its production and adaptation, the way the wires work is really very simple. The core of conductive metal, most often copper though aluminum has been used in the past, is attached to a source of electricity. This could be a production center like a power plant, or just the nodes on a 9-volt battery, the process is the same. The electrical charge is then conducted through the entirety of the wire, and will escape wherever it makes contact with something that will accept the electrical charge.
The purpose of insulating electrical wires is to keep the electrical charge in the wire. The electrical charge being passed through the wire core is trying to get out on the path of least resistance. If the wire is wrapped in a material that doesn't allow electricity to pass through it, like rubber or plastic, then the charge continues to travel down the wire until it reaches the other end. This has the benefit of both making sure that the charge travels the full length of the wire, and insulation allows people to handle "live" wires without worrying about electrocution. In this way a charge will travel down a wire to the far end, moving the electrical charge from the source, to whatever the wire is plugged into.