The picture gives information about how a central heating system works in a house.
At first, the cold water enters into the house through a pipe and migrates untill it reaches to the storage tank. The cylindrical shaped tank, called storage tank, is connected with many other pipes. One is linked with the cold water, another one with the boiler which is run by either gas or oil. The boiler is regulated by a pump and it also has connection with the cold water which is coming from other direction of the house. The boiler is the main central point where the frezzing water is transformed into hot water. Then the hot water radiators which is linked to the boiler gives a heating environment in the house with the help of its small tubes.
On the other hand, the warm water form boiler moves towards the storage tank which is also connected with the tap water and provides hot water when needed. The tank is also linked to the overflow pipe which sent back additional water to the water tank.