The design document tells HOW you will implement (or already have coded) your program.
While this is a small program and you might be able to write the code with no documents at all, there will come a time when you work on a program large enough to not be able to keep in your head all at once. This will most likely result in a big failure for you if you do not know how to use documentation to extend your brain's memorization capability. We are learning to document our programming on this small example just to start good habits.
For this assignment, you should answer at least the following questions.
1) What controls will you use to represent your board?
2) What will you use to represent each card? What control(s) will you use?
2a) How will it be represented when it is 'face down' (blank)?
2b) How will it be represented when it is face up (picture)?
2c) How will it be represented when it is done?
3) What will you use to remember what button was pushed last?
4) What control events (e.g. _Click()) will you use?
5) What logic must you follow in order to make the program run?
Note that in this document you need to describe how to write the program, not
actually write it. You should be able to give this document to me and I should
be able to build a very similar game to yours that functions identically.
Think of this document as the recipe for making the program.