Today is the birthday of the world.
Rosh Hashanah means the head of the year, and is technically one of two heads of the Jewish calendar. It is symbolized by certain foods, like apples and honey, that signify a sweet year.
Rosh Hashanah starts the month of Elul (in the Jewish lunar calendar). This is the time for preparing for the New Year, and Yom Kippur, the day of atonement that comes 10 days after Rosh Hashanah. During this time, Jews all over the world go inward, doing a moral inventory and reflecting on whom we may have hurt and who may have hurt us. Then the 10 days between Rosh Hashanah are the most important days of the year for teshuvah. That means "return," or return of the soul to its original oneness (some say atonement=at-oneness) with God.
Because Judaism is in many ways about action in this world, especially about what it means to be a good human being in relationship with others, atonement is not for sins, nor is there original sin. The word for sin means approximately "off the mark" and these 10 days are a time to get back on the mark again. We don't just think about making amends—we must actually contact people we've hurt, act on our good impulses and set the record straight. It means to take responsibility for our actions, not project them onto others, and do corrective action.