To illustrate something means to show or describe it with pictures or words so that people understand it better.
When you want to explain a complicated idea or a difficult process, you often use illustrations. You might draw a picture or create a diagram to help others visualize what's going on. For example, if someone is trying to teach kids about the different parts of the human body, they might use pictures to illustrate each section. Or, if you're writing a book about how to fix a bike, you could include illustrations of each step to make it clearer. Illustrations can also be used in art and design to add visual interest and help tell a story.
To shed light upon.
