An analogy is a comparison that tries to explain something unfamiliar in terms of something that should be familiar to the common reader. An analogy paragraph creates a vivid, concrete image in the reader's imagination, and is an effective way of communicating a foreign concept or an uncommon experience. Your reader is compelled through the analogy to better understand the idea, process, or experience you describe. Most often an analogy is signalled by the use of the word like or the phrase is like. Poet and science writer Diane Ackerman uses a familiar analogy in the following exerpt describing how the human eye works:

We think of your eyes as wise seers, but all the eye does is gather light. Let's consider the light-harvesting. As we know, the eye works a lot like a camera; or rather, we invented cameras that work like our eyes. To focus a camera, you move the lens closer to or farther away from an object. The eye's rubbery, bean-shaped crystalline lens achieves the same result by changing its shape—the lens thins to focus on a distant object, which looks small; thickens to focus on a near one, which looks large. A camera can control the amount of light it allows in. The iris of the eye, which is really a muscle, changes the size of a small hole, the pupil, through which the light enters the eyeball.