Imagine a cardboard box that is lined with blue plastic wrap. The cardboard box is like your abdominal wall.
If the cardboard is intact and the pressure inside the box increases, you never see the blue plastic wrap outside of the box.
If there is a defect in the cardboard wall and the pressure were to increase in the box, such as with straining or coughing, the blue plastic wrap would bulge outside of the box. This bulging plastic wrap is the hernia sac which fills with intestine.
The surgeons at CT Hernia Center repair the hole in the cardboard wall by placing mesh between the blue plastic wrap and the cardboard wall.