Yom Tov or festival is one day or several days observed by Jews as holy or secular commemoration of an important event in Jewish history. In Hebrew, Jewish holidays and festivals, depending on their nature, are called yom tov ("good day") chag ("festival") or Taanit ("fast").
The origins of various Jewish holidays generally lies in the Biblical mitzvot (commandments), rabbinical, and modern history of Israel.
Rosh Hashanah - the Jewish New Year
Rosh Hashanah is the Jewish New Year and Day of Judgement, in which God judges each person individually according to their actions, and makes a decree for the next year. The festival is characterized by the mitzvah (commandment) special blowing the shofar.
* During a variable number of days before Rosh Hashanah, among Ashkenazim, and the entire month of Elul among Sephardim, are added special prayers in morning prayers known as Selichot.
* Erev Rosh Hashanah (evening of the first day) - 29 Elul
* Rosh Hashanah (ראש השנה in Hebrew) - 1-2 Tishrei
Rosh Hashanah by the Mishna as the new year for calculating calendar years, the laws of Shmita (sabbatical year) and Jubilee, vegetable tithes, and tree-planting (determining the age of a tree).
According to an opinion of the Oral Torah (the Jewish oral tradition), the creation of the world was completed on Rosh Hashanah. The recitation of Tashlikh occurs during the afternoon of the first day. Orthodox Judaism celebrates two days of Rosh Hashanah, both in Israel and the Diaspora. The two days together are considered a yoma arichta, a "long day" only. A significant number of Jewish communities reformists celebrate only one day of Rosh Hashanah.
Source : http://pt.wikipedia.org/wiki/Festas_judaicas