The cut diagram and the photos should be pretty self-explanatory. In some of the photos (e.g. showing the braces under the seat), the bench is upside down. My construction is pretty loosey goosey -- these will go on beaches where a little unevennness is no big deal.
These benches are heavy! Not especially pretty, but you could saw a nice curve on the "armrests", paint them or add a cushion.