I'm going to assume that you downloaded 1.6 dev version of quiz:
First, answer the essay question(s) while logged in as a student. Then, as admin or as an editing teacher, go back into the quiz module and click on the "Manual grading" tab. From there you will see the essay question(s) in your quiz. Click on one of those and you will see a list of all the students who have answered the essay question and their attempts at the question. Click on one of those and you will be at the grading screen.
Post back if you need more help
Mark
First, answer the essay question(s) while logged in as a student. Then, as admin or as an editing teacher, go back into the quiz module and click on the "Manual grading" tab. From there you will see the essay question(s) in your quiz. Click on one of those and you will see a list of all the students who have answered the essay question and their attempts at the question. Click on one of those and you will be at the grading screen.
Post back if you need more help
Mark