After selecting a topic, spend some time thinking about what you already know about the topic. Then, think about questions you have about the given topic. Brainstorming is combining what you already know about a chosen topic and what you still want/need to know in order to write the essay. Organize your thoughts into similar categories using either a list, a web, or a mindmap. Listed below are two online tools you can use to help brainstorm your ideas.
Brainstorming Tools: