How is radiation different from conduction and convection?

Radiation is a form of heat transfer just like convection and conduction, but it does NOT require a medium.

Radiation is simply another term for light waves (not necessarily visible light), so we can transfer heat by using EM radiation, such as a microwave oven, or using a magnifying glass and focusing the sun light on a spot.

For convection and conduction, you need a medium. For conduction, the objects must be in contact with one another (like touching a hot frying pan). Conduction is the flow of heat due to fluid (gas or liquid) flow. This is why the weather people mention the "Wind chill factor". The air (fluid) flowing around you pull heat away from you faster than if the wind was not blowing.

Hope this helps. -Mr. C