Beginning 2.5 hours prior to each scheduled performance, you can enter the lottery in The Public Theater lobby by filling out an entry card with your name and indicating if you want one or two tickets. Limit one entry per person, duplicate cards will be removed. At 2 hours prior to curtain, no more entries will be accepted and winner names will be drawn. Winners must be present at the time of the drawing and will proceed directly to box office to purchase tickets. Cash only, subject to availability.
Details here.