Heat transfer Occurs when Temperature difference in the system exist. In our environment heat transfer occur all the day. Heat normally flows from higher temperature body to lower temperature body by three methods Conduction, Convection and Radiation.
When two Bodies of different temperature comes in contact with each other heat flows from flows from hot body to cold body by collision of the molecules.
In Solids molecules of hot body vibrate more frequently than cold body. When both bodies comes in contact with each other their molecules collide and some energy from hot body is transferred to cold body until both bodies attains same temperature
when you boil water on the gas stove heat is conducted to pot from fire.
It is Heat transfer that is caused by flow and diffusion of fluids (liquids, Gases) from higher temperature region to lower temperature region.
When water is boiled on gas stove heat is conducted by metal pot. Metal increase the temperature of water that is in contact with it. Hot water rise to surface and replaced by cold water. This process continues and cause circular motion.
In This process heat is transferred by electromagnetic waves known as light. This process is independent of material medium to transfer heat. In this way heat can be transferred through space. Sun transfer heat by radiation which we feel.