There are all kinds of commercially available jigs and tools to assist in making box joints (or dovetails) but I made my own jig quickly and easily with the router table at TechShop and some scrap wood.
Router table and a 1/4" straight bit
Compound miter saw or table saw
3-4" wide board
I made it at TechShop!
Step 1: Prepare the sides
Cut four sides. Label each piece lightly in pencil: front, back, left and right. It helps to put the label at the top of each piece to aid in orientation later.
If it helps, lay them out in the way they will be assembled.