A stacked dado blade set is a series of specially-designed saw blades that are to be installed onto the arbor of your table saw or radial arm saw for making partial depth cuts of various widths for dadoes and rabbets. The blade set has two full, matching saw blades along with a series of chippers, or unique blades that fit between the outer blades. Think of the two outer blades much like bread on a sandwich, with the chippers being the peanut butter and jelly (or other goodies) inside the sandwich.
To install a stacked dado blade set onto the arbor of your table saw, first disconnect the saw from power and raise the saw blade to the highest point. Then remove the throat plate that covers the wide opening (or throat) in the saw table, then use the saw's wrenches to remove the arbor nut and washer. Remove the existing saw blade and set it aside in a blade drawer or other safe location where the carbides of the blade won't be damaged.
Most stacked dado blade sets come with a carrying case that holds the outer blades and chippers together for storage when not in use. Open the case and take out the two outer blades. Notice that each of the outer blades likely has a direction indicator on one side of the blade. Hold the two blades vertically with a carbide cutting tooth facing toward you on the top edge of each blade. If you notice the outside edge that is visible on each blade, you should see the arrow pointing in the same direction as the cutting edge of the teeth. If this is the case, you have the outer blades oriented properly.
If your saw arbor requires you to slide the blade to the right on the arbor to remove it, slide the left-most saw blade from the stacked set onto the arbor first (with the face containing the arrow against the saw's arbor washer). You'll place the opposite outer blade onto the arbor last, with the arrow-side of the blade facing the arbor washer and nut that will be installed last.
Next, locate your chippers, Your set probably will have four full-sized (meaning 1/8-inch wide) chippers, and one half-sized (1/16-inch wide) chipper. The width of the dado will be determined by the number of chippers that you install. Notice that each of the chippers will have a small number of teeth, but those teeth will have a carbide cutting face that should face you when holding the chipper vertically and looking at the top edge of the blade. If you need to make a cut wider than 1/4-inch, slide one or more chippers onto the arbor (oriented so that the cutting face of each chipper's teeth are facing toward the front of the saw when installed on the arbor). For an explanation of how many chippers and outer blades to install for various widths of cut, refer to this article on stacked dado blades.
Once you have installed the requisite number of chippers, place the second outer blade onto the arbor (with the arrow side of the blade facing away from the chippers), followed by the arbor washer and nut. Tighten the arbor nut with the wrenches, then lower the blade trunnion of the saw and install a zero-clearance insert into the throat for safety.
If you need to install the stacked dado set onto a radial-arm saw, the approach is similar, but instead of removing the throat plate, you'll likely need to remove the saw blade guard and use a specialty guard that can accommodate the width of the dado blade set.
One word of caution. A stacked dado set is never to be used on a circular saw. The stacked dado set is far too dangerous to be used on a handheld saw.