Essay exams require you to analyze and synthesize what you have learned in a class, presenting it in a new form. Being able to do this means you truly understand the information the course teaches.
Even though essay exams are written under time pressure, they still require the same processes of planning, drafting, and revising you use for any piece of writing. The links below offer strategies for adapting your process to this particular context. Many of these pages also give advice on test taking in general, including advice on how to interpret questions.