Hi Guy,
Actually MDI Form is almost have similar function as normal form, but the difference is this MDI actully act as a Parent form for any other MDI Child form. So if you defined 1 new form as MDI form and 1 other form as MDI Child, those MDI Child will be display under MDI Form window by the time you load those form.
And also only MDI Form have capabilities for Menu selection in the Menu Editor.
If you want to define 1 form as MDI Child form, you can update the MDI CHild property for the specified form to true value.
Hope this will help you.
Regards,
ACE888888