No, he means that you should make your application's screens in such a way that they appear properly and are usable on a resolution of 800x600
You can most easily do this by setting the size of the form to 750x550 - that the minimum size of your form. Design it well.
If you dont know how to make your forms resize properly so that all the controls space out nicely etc, then you should ask here and we can help.
Designing in this way ensures:
Your form will still be OK and usable at 750x550 - i.e. when the user has a 800x600 screen
Your form will grow sensibly and provide users of larger screens a lot more space to work in