This being a free course there is no course submission I believe, but you can post it either here in the forum or even better and easier to add multiple images etc in the gallery with the "add yours" button.
Yes exactly as Sascha says. The other full on courses have exercise tasks for you to challenge yourself and then you can submit your result for the teachers to grade them. Press Start is only a free introductory course, so it has no tasks attached to it. But people always upload their result to the gallery or make their own polybook on the forum so they can keep their track on their progress and they upload their images there.