A circular saw is like a very powerful, spinning pizza cutter. It has a round, flat blade with sharp teeth on the edge. When you turn it on, the blade spins really fast and can cut through all kinds of things like wood, plastic, and even metal!
You have to be very careful when using a circular saw because the blade is so sharp and can be dangerous if you don't use it the right way. You always want to make sure you're wearing safety glasses and keep your fingers away from the blade.
To use a circular saw, you usually clamp the thing you want to cut down so it doesn't move around. Then you turn on the saw and slowly move it along the thing you're cutting. If you need to cut at an angle, you can adjust the saw blade to do that too.
Circular saws are really handy tools for DIY projects or building things, but you always want to be safe and use them carefully!