Dovetail joints are an ancient way of mating two pieces of wood at a corner. Often used in cabinet-making, the dovetail joint is both extremely strong, and aesthetically pleasing.
I must admit, I can make a dovetail joint, but it’s so loose as to not be usable. It’s on my bucket list of skills to learn. This video by John Bullar explains simply how to cut them. You’ll note that he freehands the angles used (probably because he’s done thousands of them), but you can also get dovetail markers to help with your first time.
Make sure you get yourself a good marking gauge and a fine saw, and you should be able to do it after a couple of hundred tries.