Dado joints are a simple way to join wood together, but they require a precision cut to be effective. If you don't have dado blade or table saw, you can still cut dado joints using a circular saw and a couple jigs. Here's how it's done.
A dado is a square-walled, flat-bottom channel cut across the grain of wood that another piece of wood will fit into snugly. These are cut using a dado blade on a table saw which removes the wood to create the channel.
A router can be used to cut dadoes, but a circular saw can also be just as effective. You'll need to make two custom fences that have the width of the edge of the circular saw shoe to the blade built into it.
The fences are then clamped onto the wood to be cut and multiple passes are made with the circular saw to remove the wood. The claw of a hammer does the final chipping.
Check out the article below, which accompanies the above video with tips on building the fences and more photos.
Cutting Dadoes with a Circular Saw [Woodgears.ca]