This paragraph develops an idea by means of a comparison with a similar idea. (Note that
analogy is a useful tool, but using it can also lead to problems.)
Light and all other forms of radiation are analogous to water-ripples or waves, in that they distribute energy from a central source. The sun's radiation distributes through space the vast amount of energy which is generated inside the sun. We hardly know whether there is any actual wave-motion in light or not, but we know that both light and all other types of radiation are propagated in such a form that they have some of the properties of a succession of waves.
When you are writing an analogy, you must understand the things you are comparing. Do some research and look up facts if you need to! Then, make a list of all the ways your subjects are alike. Make these into complete sentences and you have a paragraph.