Cut twelve pieces of 1-by-3-inch lumber to measure 16 inches long each. Glue three of the 16-inch pieces together to form a thicker piece of lumber. Rip cut the piece so that it is 2 inches wide by 2 inches thick. This will be one leg of the bench. Repeat to create the remaining three legs.
Cut two more pieces of 1-by-3-inch lumber to measure 12 inches long. These are the side support boards.
Place two of the legs parallel to each other and 12 inches apart. Place one of the side support boards in between. Attach both the legs to the side support using wood screws. This is a side structure. Repeat to create a second side structure.
Cut two long rails from 1-by-3-inch lumber to measure 43 inches long. Set the side assemblies up on the legs, with the side supports on top, 43 inches apart from each other. Place one of the long rails across the two side structures, in line with the side supports. Screw the long rail to the side structures with 1 5/8-inch screws. Repeat on the opposite side.
Cut three 16-inch long boards from 1-by-3-inch lumber. These are the center supports. Attach one of the boards across the bench in between the two long sides in the center of the board. Repeat on either side of the center support. These are the seat supports.
Cut six seat slats measuring 47-inches long, from 1-by-3-inch lumber. Evenly space the seat slats across the bench parallel to the long rails. Attach the slats by screwing into the seat supports with 1 5/8-inch screws.
Add a little glue to the end of 3/8-inch dowel rod. Stick the rod in one of the screw holes made. Cut the rod off, flush with the wood using a handsaw. Repeat for each noticeable screw hole.
Sand the entire bench.
Spread an even layer of wood stain over the entire bench using a paintbrush. Allow the stain to dry completely.