Short answers, pulled from the story.
The Reformation was a major theological movement in Western Christianity in 16th-century Europe that challenged the papacy and the authority of the Catholic Church hierarchy. It marked the beginning of Protestantism and is counted among the events that ended the Middle Ages and opened the early modern period.
The Reformation is usually dated from Martin Luther's Ninety-five Theses in 1517. On the 31st of October 1517, Luther addressed a letter to Albert of Brandenburg attacking the preaching of indulgences and attached the Ninety-five Theses to it.
Luther opposed the indulgence campaign launched to fund the new St. Peter's Basilica in Rome. The Dominican friar Johann Tetzel used aggressive methods, with a slogan claiming that as soon as the coin into the box rings, a soul from purgatory to heaven springs.
The printing machine with movable type allowed rapid dissemination of religious materials in the vernacular. Luther was responsible for about one-fifth of all works printed in Germany in the first third of the 16th century, and statistical analysis links the presence of a printing press in a German city to the adoption of the Reformation.
Historians customarily refer to John Wycliffe and Jan Hus as forerunners of the Reformation. Wycliffe attacked pilgrimages, the veneration of saints, and transubstantiation, while Hus was burned at the stake on the 6th of July 1415 after the Council of Constance.
The Counter-Reformation was the Catholic response to the Reformation. The Council of Trent met in sessions from December 1545 to 1548-1551 to 1552, and 1562 to 1563, reaffirming apostolic tradition as a source of faith equal to the Bible and stressing the importance of good works in salvation.
The term Protestant arose at the Diet of Speyer in 1529, when five imperial princes and fourteen imperial cities issued a formal protestatio against the reinforcement of the imperial ban on Luther. They were mocked as Protestants, and the name spread to all followers of the new theologies.