During the Middle Ages, there was always a power struggle between the many different kings and the church. Both wanted to have the final say over what was going on in Europe.
Almost everyone was Christian. It was called the "Golden Age of Faith." All Christians followed the Catholic Church in Rome and its' leader, the pope. Everyone was required to go to church (also called mass). This mass was said by a priest and he led people in prayer. Holy days gave people a day off from work. This is where the word "holiday" comes from.
The pope had other helpers besides priests - they were bishops and cardinals. They oversaw all the churches and said mass in a cathedral. Still, the main leader of everyone was called the pope. He was to be obeyed by all since he was the spiritual leader of the church. Even the kings listened to the pope.
Monks were men who devoted life to their religion. They lived in monasteries and might later become a priest. The women who did this were called nuns. Nuns lived in convents. Monasteries and convents were for prayer, religion, and learning. Monks and nuns made books by hand until the invention of the printing press.
The church and the people running it had great power. The pope was supposed to be the best example of a Christian person and a good spiritual leader. However, the church made poor and unfair decisions. For example, they started to focus on money. They "sold" forgiveness. These were called indulgences and if a person paid money their sins would be forgiven. The church spent money on art that was not necessary. They built palaces for themselves. Leaders of the church also gave better jobs to their relatives and they even gave church money to their relatives. This money (donations collected from everyone) was supposed to be spent wisely but it was not.
This made many people very angry. In 1517, A German man named Martin Luther wrote a list of 95 arguments against the church. This list (called the 95 Theses) was copied and spread due to the invention of the printing press. Eventually, this led to a different type of Christianity called the Protestant Church which came from the word protest. Later, many other Protestant churches would be formed. Martin Luther's protest is called the Reformation because it tried to reform the ideas of the church.
King Henry the VIII has a famous church story too. The pope refused to let Henry VIII get a divorce from his wife because it was forbidden by the church. Henry wanted to marry someone else to try and have a son. When the pope refused, Henry the VIII started his own church called the Anglican Church (or The Church of England). Henry VIII would end up having 6 different wives and killed 2 of them. He wasn't a great example of a husband or church leader.