Design mode allows you to define a form directly in the UserForm window of the VBA IDE, while Run mode allows you to make changes to a form dynamically using the code of a program.
While you are building your form you are working in Design mode, where you can
While in Design mode there is no interaction among the user, the user interface of AutoCAD, and your form.
Once you run your application, or your user runs your application, the form is then in Run mode. While in Run mode you cannot make adjustments to the form directly. However, the form is now displayed in the AutoCAD user interface and the user can interact with the form as part of the normal operation of your application.