Read the question at the top of the screen, then answer it by clicking on the number of the question that fits you best. After all the questions have been answered, click on the "What house am I in?" button to see which Hogwarts house you are in!
Thanks @marimineck. I added cloud variables so that people will know how many other people are in their house. Sorry new scratchers, you won't be able to add to the total number of people in their house.