Imagery:
Sensory details or figurative language used to describe, arouse emotion, or represent abstractions. May use terms related to the five senses: visual, auditory, tactile, gustatory, or olfactory.

Example:
"In November he finished his last rations. He felt weak and dizzy; chills racked his gaunt frame. Hands and nose continued to get worse as do feet. Nose tip very swollen, blistered, and scabbed... This is sure a slow and agonizing way to die."
-Into the wild, Jon Krakauer

Explanation:
Krakauer describes McCandless using imagery, so that the reader knows what he looks like and what he is going through. The reader can get a clear picture of what McCandless looks like, therefore helping them characterize, and see what is happening to him. Also this type of imagery is very in depth  and tells the read how awful he looked, making the reader feel bad for McCandless, and ponder on to why he did what he did. Which is Krakauer's main purpose of his novel .