Woodworkers reach for a hole saw when they need to make circular openings between 1 1/2 to about 5 inches in diameter. They have a choice between a spade bit and hole saw for diameters between 1 and 1 1/2 inches, and usually use a jigsaw to make large holes. A hole saw, which has teeth arranged on the outer edge of a metal cylinder, can generate a lot of torque -- especially if it's a large saw -- so it's important to mount it correctly in the drill to avoid slipping, wobbling and kickback.
Choose an appropriate pilot bit. Hole saws usually come in a set that includes several pilot bits -- from 1/4 inch to 7/16 inch in diameter. Consult the manual for the proper bit to use.
Insert the bit through the hole in the bottom of the hole saw and slide the saw onto the mandrel, the metal fitting that holds the bit. If you have a newer hole saw set, you can simply snap the bit onto the mandrel. If your set is an older one, you'll probably have to screw it on. It's a forward thread, which means you screw the saw clockwise to tighten it onto the threads.
Hold the mandrel with one wrench and grip the base of the saw with another. Use the wrenches to tighten the saw onto the mandrel. Failure to do this could result in the saw coming loose while you're using it.
Disable your drill by unplugging it or removing the battery. Open the chuck far enough to insert the base of the saw mandrel into the drill. Hold the saw by its base while you tighten the drill chuck, either by turning it with your hand or using a chuck key, depending on the drill. Tighten the chuck as much as you can to prevent it from opening while you're using the saw.
Rotate the chuck a few times by hand to make sure the saw is centered. When you're satisfied, plug in the drill or insert the battery, and start sawing.