If people were in the middle of a fast, and the rain they were asking for did fall out, they could say that it fell in their merit and stop fasting. There are multiple opinions on this, but the story of Shmuel the HaKatan represents one extreme. (He called himself HaKatan, the Small One, although he was the most excellent sage of the generation.)
Once, the rain fell before the daybreak. People felt tremendous, but Shmuel said it was similar to a master who said, "Give them whatever they ask, but let me not hear their voices." Another time, rain fell after the end of the fast. People felt good, but Shmuel told them it was similar to a master who said, "Wait till my servant is humbled enough and only then give him what he needs." If so, when should the rain start to be considered good, according to Shmuel? He answered, "When the prayer leader says, "Who makes the wind blow" - and the wind blows. Then, the prayer leader says, "Who makes the rain fall," and the rain falls.
The Talmud enumerates the rules of communal worship, days of fasting, and days of feasting. When the Temple was in existence, groups of priests served on appointed weeks. Community representatives were also there, in the Temple or their cities, as if standing by their offerings. These were called "maamadot" or "standing." The saddest day of the Jewish calendar is Tisha B'Av, and the most joyful days are Tu B'Av and Yom Kippur. The following pages will give more details.
Art: The Yerres, Rain by Gustave Caillebotte