I agree with Richard's comment. The best way to make your point in an essay is with a strong but fairly simple argument; not a bunch of ideas thrown together without any sort of sense or order. Another way of looking at it is: if someone is reading your paper, they can see the shape of your argument if it is well-written and they can understand what your point is. They will not see the shape if there's too much going on without any thought put into it. I hope this helped a little!

Basically, the instructor is saying that too many essays just blather on and say a lot of things without having a clear, logical flow that connects the ideas. If you just start your answer by writing down the first idea that comes to mind and then add another idea and then another, you will wind up with a jumbled mess. You wouldn't build a house that way so don't build an argument that way either. Instead of you just writing everything that comes into your mind, the instructor wants you to think about how to answer the question before starting to write. Try to develop a vision of how the different ideas will fit together to answer the question. So, for example, do you have one single argument with several supporting pieces of evidence? Do you have several arguments, perhaps one or two principal arguments and a few minor ones? Or do you plan to rebut the objections to your argument? These are different shapes that your answer can take. Plan out what you are going to write before you write it so that the reader does not get confused and lost by a disorganized jumble of ideas that do not seem related to each other.

Form is possible but not perhaps more ambiguous. Form could lead the reader to think in terms of whether it should be in the form of a speech, in PowerPoint form, in bullet points, in conventional essay form, etc.

All that is very good advice indeed, though I would not be surprised if AnotherWorld's objective was to get the comprehension exercise over and done with rather than learn the art of writing or digest and then implement the writer's advice.

It means "structure and flow".