Gather the four thickest boards in the kit, those without any grooves cut in them.
Arrange the boards in a rectangle. In most kits, these boards have been predrilled with pilot holes to accommodate the screws. If only one face of the boards is painted, set the painted faces facing outward.
Use the screws that come in the kit to connect the frame. Some newer kits use screws with a hexagonal head rather than a Phillips head. Most such kits come with an appropriately sized Allen wrench. If not, the head will be a standard size.
Gather all the boards in your kit that have grooves cut in them. For most kits this will be all the remaining boards.
Slide the boards together at the grooves, forming a tic-tac-toe-style pattern. This process is often easier if you soap the inside edges before beginning. In some kits, a few of these boards will be painted only on one side. Use those boards for the horizontal shelves and face them with the paint side up.
Slide the assembled cubby grid into the frame. Some kits may have pilot holes drilled through the frame to allow you to screw them into position. Others leave them free-standing, which is normally no problem unless you're tilting or moving the cubbies.
Gather your backplate. This is often a single sheet of cardboard or pressboard the same dimensions as the full cubby unit. In some kits, it will consist of several pieces. Some even provide only enough backplates to cover some of the individual cubbies.
Set the backplate against the rear of your cubby unit. If one edge of the unit is unpainted, attach the backplate to that edge.
Nail the backplate into position using the finishing nails that come with the kit.