Cutting the Pieces
Cut two 4-foot pieces from one 2x4 board for part of the frame.
Cut two 3-foot 9-inch pieces from the other 2x4.
Cut four 3-foot pieces from the 4x4s for the legs of your table.
Assembling the Stand
Construct the frame for the stand from the four 2x4 boards. Lay both 4-foot pieces on edge parallel to each other, 4 feet apart. Insert the 3-foot 9-inch boards between them, forming a 4-foot square frame. Attach the frame together by driving two 2 1/2-inch screws through both ends of the 4-foot sections into the shorter ones.
Align the square plywood top over the frame. Drive 1 1/2-inch screws down through the top every 6 inches all the way around the edge into the frame.
Attach the four legs. Turn the finished portion over. Sit a 3-foot 4x4 piece on end against each inside corner. Drive 2 1/2-inch screws through the frame into them. Use two screws on both sides of the frame that each leg touches.
Sit your table up on the legs. Drive two 1 1/2-inch screws down through each corner of the table's top into all four legs for extra sturdiness.