How can we make a simple electric bell ?

 You wind some wire around an iron rod to make an electromagnet. You arrange for a spring loaded bell clapper of iron or steel so the magnet can attract it. You connect one end of the coil to stationary end of the bell clapper. The other end goes to one side of the battery. A wire from the other side of the battery is fastened so that the middle fo the clapper will touch it when there is no current and allow the clapper to break the connection when it is attracted to the magnet.

When you first hook up the battery, current in the coil will attract the clapper which will break the circuit and release the clapper which will then make contact and allow current to flow in the coil again. This cycle will repeat rapidly to allow the clapper to ring a properly positioned bell.