Just the same as all calendars around the world, the Jewish calendar is sprinkled generously with festivals. Most of these occur on an annual basis, although some are more frequent.
The Jewish calendar is split into 12 months, based on the lunar cycle. To bring it in line with the seasons, however, a thirteenth month, Adar Sheni (literally the "second Adar") is frequently added. The Jewish New Year starts around September, the exact date never being fixed because of differences between the solar and lunar calendar.
The months progress as follows:
Tishri, Cheshvan, Kislev, Tevet, Shevat, Adar, (Adar Sheni), Nisan, Iyar, Sivan, Tammuz, Av, Ellul.
The New Moon which brings in the new month is called "Rosh Chodesh" (translated as "Head (of the) Month"). On Rosh Chodesh, parts of a special prayer called the Hallel (which consists of selected psalms) is read. As a reward for not donating jewellery in the making of the Golden Calf after the Exodus from Egypt, tradition dictates that women need not work on Rosh Chodesh.
A Luach is a booklet which contains all the dates of the festivals so that we know when to observe them.