During the afternoon of the first day occurs the practice of tashlikh, in which prayers are recited near natural flowing water, and one’s sins are symbolically cast into the water. Many also have the custom to throw bread or pebbles into the water, to symbolize the “casting off” of sins. In some communities, if the first day of Rosh Hashanah occurs on Shabbat, tashlikh is postponed until the second day. – Wikipedia