The passage stays on the left — scroll it as often as you like, including after you answer. Questions appear on the right, one at a time.
Choose an answer and press Check answer. You'll be told straight away whether you were right, what the correct answer is, why the tempting wrong answers don't work, and how to read a question of that type next time. Then move on to the next question. Your marks are added up at the end.
There are 38 questions: comprehension, spelling, punctuation and grammar. There is no time limit; the clock just shows how long you take.