First, brainstorm. Sit down with a pencil and paper and write down every idea that comes to you without stopping to question whether this is a good or bad idea. After you have done this for some time, then you can look back at your list and decide which ideas can be used in your essay.
Another technique you might try to get yourself started is freewriting. Sit down with a pencil and paper, set a timer for 15 minutes, and then just start writing. Don't try to write an essay. Don't worry about spelling, grammar, and punctuation. Just write whatever comes to mind about the topic. If you go blank, keep writing. You can write the question over and over again until your brain unfreezes.
Once you have a better sense of what you think about the question, then you can start to think about outlining and then drafting an essay. But you've got to explore your thoughts -- in words, on paper -- first.