What do they do in rosh hashanah?

It celebrates the Jewish new year -- the day that God created Man in his own image (ostensibly 5769 years ago). It is the holiest day in Judaism.

Rosh Hashanah is the Jewish new year. The Jewish calendar is different than the Julian calendar used in America.

Rosh Hashanah is the Jewish new year. Rosh Hashanah literally translates to 'Head of the year'.

Rosh Hashanah was on October 3rd in 1959.

Rosh Hashana is always observed on the first day of Tishrei in the Jewish ritual calendar. The next occurrence will begin IY"H at sunset on Wednesday evening, September 8, 2010.