Short answers, pulled from the story.
Martin Luther started the Lutheran movement on the 31st of October 1517 when he nailed ninety-five arguments to the door of the Castle Church in Wittenberg. This document challenged specific practices of the Roman Catholic Church such as the sale of indulgences and the authority of the Pope.
Johann Maier von Eck publicly labeled Luther's followers as Lutherans during the Leipzig Debate in July 1519. The term began as a derogatory label intended to mark them as heretics before becoming the standard identifier for the movement itself.
The Book of Concord is a collection of ten documents that unified all German Lutherans under identical teaching and was published in 1580. It replaced earlier incomplete collections of doctrine after over eight thousand leaders signed the Formula of Concord to resolve internal disputes.
Prussia adopted Lutheranism as its state religion in 1525 while monarchs in Denmark-Norway and Sweden embraced the reforms to gain control over church properties. King Christian III of Denmark advanced the Reformation after winning a civil war in 1536.
Lutherans believe individuals receive salvation through faith alone which is the knowledge acceptance and trust in Christ created by the work of the Holy Spirit. This gift of salvation comes from the grace of God made manifest in the birth life suffering death and resurrection of Jesus Christ.