On Tisha Be'Av, Jews fast and mourn for about 25 hours, starting from sunset until nightfall the next day. The Book of Lamentations (Megillat Eicha), in which the prophet Jeremiah laments the destruction of Jerusalem and the subsequent exile is read as well. Washing one's body, anointing oneself, wearing leather shoes and engaging in marital relations are all forbidden on Tisha Be'Av.
Tisha Be'Av marks a number of calamities throughout Jewish history. The day that the 12 spies gave a slanderous report about the Land of Israel to the Jews in the desert, leading to that generation being forbidden from entering the land, is traditionally believed to have occurred Tisha Be'Av.The Talmud recounts that when the Jews cried out in response to the spies' report and even expressed a desire to return to slavery in Egypt, God responded, "You wept needlessly, and I [will] establish for you [a night] of weeping for [future] generations."
Both the First and Second Temples in Jerusalem were destroyed on Tisha Be'Av.
A number of other calamities occurred on or near the ninth of Av, including the expulsion of the Jews from England, France and Spain, the beginning of World War I, the formal approval of the Nazi's Final Solution, the mass deportation of Jews from the Warsaw Ghetto to concentration camps and the First Crusade.
After using the bathroom or when washing your hands in the morning, one should only wash up to the knuckles. If your hand is dirty above the knuckles, this may also be cleaned.
Deodorant is generally not considered as a forbidden ointment as it is not considered pleasurable.
Studying Torah, except for melancholy passages or laws of mourning and Tisha Be'Av or Musar (Jewish morals), is forbidden on Tisha Be'Av.
On Tisha Be'Av, people should not greet one another with verbal greetings. Sitting on a chair is forbidden until after halachic midday (shortly before 1 p.m. in Jerusalem and Tel Aviv on Sunday). Sitting on the floor or in a low chair is permitted.
On the morning of Tisha Be'Av, men do not wear a tallit (prayer shawl) or tefillin (phylacteries). The tallit and tefillin are put on during the Mincha (afternoon) prayers.
As the fast is beginning on Saturday night, some of the laws concerning the day of mourning are different than when it occurs on other days.
Starting from sunset on Saturday, all eating and washing is forbidden. All the restrictions of Tisha Be'Av begin at sunset, except for the prohibitions on leather shoes and sitting on a chair which begin after Shabbat ends.
Only the blessing on the Havdala candle is recited on Saturday night, with the rest of Havdala (except for besamim) recited after Tisha B'av ends on Sunday night. One should not eat until the rest of Havdala is recited.
Any questions or uncertainties should be clarified with your rabbi, as some customs differ between communities.
Fast Start and End Times: (According to MyZmanim. There are varying customs)
Jerusalem
Start: 7:49 PM
End: 8:15 PM
Tel Aviv
Start: 7:47 PM
End: 8:17 PM
Haifa
Start: 7:48 PM
End: 8:19 PM
Eilat
Start: 7:41 PM
End: 8:10 PM
Beersheba
Start: 7:45 PM
End: 8:15 PM
New York
Start: 8:24 PM
End: 9:13 PM (According to Rabbi Moshe Feinstein, those who have trouble fasting may eat at 9:03 PM)
Los Angeles
Start: 8:03 PM
End: 8:46 PM (According to Rabbi Moshe Feinstein, those who have trouble fasting may eat at 8:38 PM)