Eight rounds of each exercise, 20 second interval bouts, 10 seconds rest. You then get 1:00min rest before you begin the next eight rounds.

So it looks like:
8 rounds of pull ups, 1:00 rest, 8 rounds of push-ups, 1:00 rest, 8 rounds of sit-ups, 1:00min rest, 8 rounds of squats, 1:00 rest, 8 rounds 500m row, Done.
You can do the exercises in any order but all eight bouts must be done in a row.

Notes:Tabata et al. found that interval bouts comprised of 20 seconds with 10 seconds of rest placed significant anaerobic demands on the subjects (the accumulated oxygen deficit was 69 ml/kg) allowed them to reach their anaerobic capacity. Tabata et al. determined a four minute interval training session done at 170% of an individuals VO2MAX is the equivalent of a maximal anaerobic effort.