Rosh HaShanah is the first day of the year. It is the day our fate is written. Hashem is giving us a chance to repent on Rosh Hashanah, and through the tens days of atonement. Yom Kippur is the day our fate is sealed. So we must pray hard on these days. We blow the shofar 100 times in that day. There are customs to, dip an apple in the honey, and so on. The main purpose it have a Shanah Tova U'metukah!