Measure in 6-inches from each end of the 36-inch 2-by-4s. Line one 4-by-4 at each location. Hammer in four 5-inch nails through the 2-by-4s into the top of the 4-by-4s.
Measure in 6-inches from each end of the six 2-by-6s and mark these locations with a pencil. Set all six boards next to each other horizontally so the boards form a rectangular surface measuring 36 inches by 48 inches with the measurement marks facing up.
Cover the nailed side of the 2-by-4s with a layer of wood glue. Line the two 2-by-4s vertically against the rows of 2-by-6s at the 6-inch marks.
Flip the structure over to standing position so the 4-by-4s act as legs for the table. Hammer two 3-inch nails evenly spaced into each 2-by-6 at the 2-by-4 location.
Paint the table with polyurethane using the large paint brush. Allow polyurethane to dry completely before using the table. Apply second coat if necessary.