When I write I see the characters running about, playing, sharing conversation, laughing, crying, and having the adventures forming the narrative of their story. I also see their colorful little houses, and the beauty of the sky and grass and trees and ponds where they live.
When we read we do the same, and the images we imagine are of our own making, drawn from our own experiences, and are therefore part of a personal world only we can inhabit. There is an amazing magic in all of this. The squiggly little shapes on a page present to us a chance to create and travel to places no one has ever seen, and to share a glimpse of the lives of characters whom we could not otherwise have a chance to meet.
In addition to writing I love to simply sit down to my desk with a pencil in hand and draw. Naturally, after spending so much time with the characters in the stories, I enjoy having them present in some form, even when not writing, to have something remind me of their personality and appearance, if only in the form of a picture. Of course the drawings are only suggestions, readers may “see” the characters quite differently, and that is part of the magic.