When you put your heating on, the gas from your boiler enters a combustion chamber and an electric ignition lights the gas. The heat from the gas is used to heat water carried in a pipe. This network of water pipes will connect to all radiators in your home.
A radiator is essentially a copper pipe bent back and forth to give a large surface area so more heat can be radiated into the room. Radiators should really be called convectionators as 80% of their heat is lost by convection, not radiation. Of the 20% of the heat that is radiated, 10% goes out of the front of the radiator and the other 10%, is radiated out of the back and mostly absorbed by the wall. The heat that is convected rises upwards and tends to get trapped at the ceiling or is lost out of the window.
This is where a Radfan can help you. It sits neatly on top of your radiator and redirects the convected heat into the heart of the room, giving you warmth where you want it.