Rosh ha-Shanah is the first day of the seventh month of the Hebrew calendar. Because the seventh month was the one in which the Israelites celebrated the harvest festival (Sukkot, when the moon was full) an announcement was made at the start of that month to remind them that they needed to finish gathering in their crops. That announcement was made by means of the blowing of the shofar, the ram’s horn.

In our post-agricultural society, the focus of Rosh ha-Shanah has switched from a time to gather in the harvest to a time to gather our thoughts and contemplate spiritual renewal and a return to a path that is more in tune with what Jews believe that God requires of us.

Rosh ha-Shanah falls on the first day of the seventh Hebrew month (Tishri), which is usually in September.
The main feature of Rosh ha-Shanah is the sounding of the shofar, the ram’s horn. This takes place towards the end of the morning service. Some of the prayers in the Rosh ha-Shanah service differ from the regular weekly and Shabbat prayers, to focus more on the quest for repentance that is a feature of this day, and it continues until the conclusion of Yom Kippur ten days later. The covers of the Torah scrolls are usually changed to white, to emphasise the yearning for purity.
The main distinction between Liberal and Orthodox observance centres on the fact that Liberal Jews observe only one day. In Orthodox Judaism there is a prohibition on blowing the shofar on Shabbat; if Rosh ha-Shanah falls on Shabbat (as it frequently does) the shofar can only be sounded on Orthodox congregations on the second day, the Sunday. Because Liberal Jews observe only one day, the shofar is sounded on that day, regardless of whether it falls on Shabbat or not.
It is traditional on the eve of Rosh ha-Shanah to eat apple dipped in honey, to symbolise the hope for a sweet year ahead. Similarly honey cake is a traditional food at this time.