Welcome, Stormy 5438.
Try this site Brainstorming Techniques.
Diagrams are more complex than listing or mapping techniques; they are good for assignments where you are required to supply more of the papers structure.
1. Write your topic inside a circle in the middle of a sheet of paper.
2. Draw a number of "spokes" radiating from the circle outwards - about five or ten of them.
3. Label each of these spokes with a question related to your topic, such as "What is it?" "How does it work?" "Who or what does it affect?"
4. Add potential answers or responses to these questions at the end of each question-spoke. Don't just fill in one answer per question; some questions can generate many potential answers.
5. You can then turn each "answer" cluster into a circle with spokes of its own, with more question "spokes" coming off of them and generating more answers/responses.
Hope that helps.