Electromagnetic radiation comes in a wide range of frequencies. You are familiar with light and radio for example but if you go higher than visible light in frequency you get to "ultraviolet" which gives you a sunburn. If you go lower in frequency you get "infrared". Infrared is heat photons. Anything at a temperature above absolute zero radiates (see "black body radiation") but a burning fire or a bright red heating coil for example produces tons of infrared photons as well as the slightly lower frequency red light you see. These infrared photons are absorbed by your skin and make you warm.
