Place plywood section on a flat surface, running horizontally. Place one 2-inch 2-by-4 section at each corner running along the left side 18-inch edge. Drive two 2 1/2-inch screws through each 2-inch section of 2-by-4 to attach it to the plywood.
Set the two 28-inch 2-by-4s directly on top of the 2-inch sections. The two 2-by-4s should stand upright into the air. Place one door hinge along the right side of the 2-by-4 edges. Attach one of the hinge flaps to the 2-inch section of 2-by-4 and attach the second hinge flap to the side of the 28-inch 2-by-4 section using 1/2-inch screws.
Place one 30-inch 2-by-4 along the right side 18-inch edge, standing in an upright position. One 30-inch section should be positioned at each corner corresponding to the 2-inch and 28-inch sections along the opposite 18-inch edge.
Place one door hinge along the left side of the 30-inch 2-by-4 sections. Attach one of the hinge flaps to the base of the 30-inch section of 2-by-4 and attach the second hinge flap to the bottom side of the plywood section using 1/2-inch screws.
Fold the 30-inch plywood sections over the plywood base. Fold the 28-inch sections over the 30-inch sections, allowing them to lie flat on top of the 2-by-4s. Unfold all four legs and place on a flat surface to use the table.