In the Essay question type you are asking the quiz taker to write a short essay. You set the subject of the essay in the Question Body box. You can specify length of the essay by entering a number of Lines in Essay Box.
Essay questions are not automatically scored and so the feedback for these questions is limited to a single piece of text, written in advance. You can edit this or switch this feedback off in Display Feedback Page for Essay Questions in Quiz Options – Other Labels.