Jesse is an artist who tries to understand the world through his drawings. They appear as illustrations throughout the book, which is designed so that it feels like we're paging through his sketchbook. This isn't just a unique approach to book design, though—art is a major player in Jesse's life.
On one level, Jesse's art provides him respite from the violence in his neighborhood, which is super stressful. Drawing helps him express himself and explore the world around him, helping him make sense of confusing things, like the ways in which Rise has changed. In this way, Jesse's drawings represent serenity and happiness.
On another level, though, his drawings also represent truth. Not because he draws things in a photorealistic way—he doesn't like to, even though he can—but because he uses drawing as a means of identifying deeper truths about his subjects:
My dad likes that—to see a picture and say something about how it looks almost like a photograph. But what I want is to draw a picture where I can see more about what I drew than just what it looks like. (11.85)
Jesse knows that looks can be deceiving and superficial. For instance, you can't tell that Mrs. Johnson, Rise's grandmother, has Alzheimer's just from looking at her—in fact, she's always smiling. So in Chapter 8 Jesse draws her as sad, with her hair floating upward and away from her head, like lost thoughts. And just as this image reveals the "real" Mrs. Johnson, his drawings throughout the book do so time and again.