This is to Exercise Your Diaphragm
What you have to do is get a binder or a book. Lay down on the ground or on a flat surface and place the binder or book on your stomach and start singing.
Sing exercises like the scales in this website. If you use your diaphram correctly, your stomach will rise and fall as you are singing, and the book will probably fall off your tummy. If there is no movement, then you are probably not using your diaphragm that much when you sing.
Try it and see whether it works!