To connect the ends of the tray to the sides, we'll use through dovetail joinery. You'll need a router with a straight bit and a dovetail bit along with your dovetail jig to complete this step of these free woodworking plans.
Follow the instructions that accompany your dovetail jig to ensure proper spacing of the tails and pins in the two-inch ends of the sides and end pieces. You'll likely end up with only one full tail on one piece and two pins on the other.
Cut the tails first, then cut the pins to fit the tails. Dry fit the assembly together to ensure a quality fit. The dovetails should fit together snugly but not so tightly that they can't be pulled apart.