As you know, symbols represent something else. For example, a flag might represent freedom. In this novel, if you look at the first several drawings, you can see that for Junior, the main character who calls himself a cartoonist because words are too limiting, art is his expression of himself. The art represents his dreams, his hope of escaping the reality of his life, and his desire to escape the reservation. Rowdy, his only friend, laughs at his jokes and cartoons, and represents his desire to be liked, have more than one friend, and leave behind the anger that Rowdy feels when his father hits him. His sister is another symbol of dreams that die and fade away on the reservation. She was going to be a writer, was a good student, but gradually gave up her dream, and instead hid in the basement from a real life. Junior has to decide if he is going to be like her and give up his dreams or fight for what he wants through school and basketball. Now I'm sure that you can easily find many more rather than use what I have given you, which are all from the beginning of the book. You can look at the middle or end and find symbolism firmly embedded in the novel.