The function of a driver is quite different from the function of an iron. The same goes for putters, hybrids, and wedges. But the grip is generally the same for all of them.
The instructions in this guide pertain to drivers. When handling an iron, remember that irons are shorter than drivers. Because of this, you don't need as much rotation on your swing, and you'll need more control.
Irons are for shots you want to strike solidly. They are for distance control. The actual grip, however, won't change much between the two.
The only club in your golf bag that will require a different grip is your putter.