Jang,
The concept of the form manager is not a complex one but showing details of how to impolement one is complex. As a matter of fact it takes a full chapter in Steve Sawyer and my book "Effective Techniques ...". You can get the book from
www.hentzenwerke.com if you are interested. It covers form managers and a whole lot more of the techniques of application building with VFP.
If you examine any of the commercial framework products for VFP you will see examples of form managers in a variety of shapes and sizes. The full details are just a little too big for a forum message to cover.