A series of fissions is called a chain reaction. If enough uranium is brought together under the right conditions, a continuous chain reaction occurs. This is called a self-sustaining chain reaction. A self-sustaining chain reaction creates a great deal of heat, which can be used to help generate electricity. Nuclear powerplants generate electricity like any other steam-electric powerplant.
Water is heated, and steam from the boiling water turns turbines and generates electricity.
The main difference in the various types of steam-electric plants is the heat source. Heat from a self-sustaining chain reaction boils the water in a nuclear powerplant. Coal, oil, or gas is burned in other powerplants to heat the water. The concept of the atom has existed for many centuries. But we only recently began to understand the enormous power contained in the tiny mass.