Cut the 2" x 6" x 8 ft common board in half. These two ~4 ft pieces will become the top of the bench. If needed, make additional cuts to get them to the same length.
Cut the 2" x 4" x 8 ft common board into four 6" pieces and four 15.5" pieces. These will be made into legs. Again, make adjustments to get them to be the same length, if needed.
This is what you will have by the end of this step: