They celebrate Havdalah.
The blessings of the Havdalah ceremony mark the end of Shabbat.
The 3 stars in the sky say that Shabbat is over.
Every Saturday at sundown
At a shabbat service at your home or at a synogauge you may light the shabbat candles and say the shabbat blessings. Also some people follow it with hallah and/or a kiddush.
The spice box is not actually passed around until the very end of Shabbat. It is passed around toward the end of the concluding service of Shabbat, called Havdalah. One tradition explains that on Shabbat, each person is given an extra soul. The passing of the spice box at the end of Shabbat makes the loss of this extra soul a little less painful.
Shabbat ends on a Saturday night after nightfall. During that time Jewish people light havdalah candles and then dip them in wine to burn them out.
Yes only when Shabbat is over. For conditions of life and death, it is permissible to do "work". For example, ambulances still run on Shabbat because people could be seriously injured on Shabbat and need medical help.
If a public fast falls on Shabbat, the fast is delayed until Shabbat is over. The one exception is Yom Kippur. If a public fast falls on Shabbat, you fast the entire day until the end of the fast, even though it means entering Shabbat while fasting.
Shabbat ends of its own accord at the time a bit after sunset on Saturday night. Nothing that mankind does can either extend it or cause it to end. Those who observe the Shabbat can only mark its beginning and its end as they occur. The brief ceremony and set of blessings that mark the very end of shabbat are known as "HAHV-da-LAH", meaning "division" or "boundary" in Hebrew. It marks the boundary between holy and weekday-like. The moment is considered to be a let-down.
Your Hebrew calendar should have the information.
No - Havdalah is the service at the end of Shabbat.
Shabbat ends in New Jersey on Saturday at sunset. You can check the specific time for today by looking up the sundown time in your location.