The purpose of the battery in a series circuit is to give the circuit a source of energy.
The purpose of a switch in a series circuit is to make it easy to open or close the electrical circuit, turning the flow of electricity on or off.
A light bulb in a series circuit is used to determine whether or not electricity is flowing.
The purpose of the wires in a series circuit is to allow the electricity to flow from one device to the next. Wire is used to carry the flow of electrons. Metal wire is a very good conductor. Materials that do not allow electricity to flow through are called insulators or non-conductors.