Although conduction does occur in liquids and gases also, heat is transmitting in these media mostly by convection. In that phenomenon, the real motion of the material is responsible for the heat transmit. Familiar examples added hot-air and hot-water home heating objects, the cooling objects of an automobile engine and the flow of blood in the system.
You probably have warmed your hands by taking them over an open flame. In that condition, the air directly above the flame is expands and heated. As a result, the density of this air reduces and then air rises. Air flow at a beach is an example of easy convection. When the heated substance is forced to move by a pump or fan, the process is called as forced convection. If it were not for convection present, it would be very hard to boil water. As water is boiled in a kettle, the boiled water expands and arises to the top due to its density is lowered. At that same point, the denser, cool water at the end surface sinks to the bottom of the kettle and is heated.