A monk getting tonsured
August 2016 - Sometimes when a little boy seemed especially smart, his parents would take him to a monastery and leave him there to be taken care of by the monks and educated, and when he grew up he would become a monk. One example is Thomas Aquinas. Monks (pronounced MUNKS) were men who devoted their lives to the service of God and of the Catholic church (there are still monks today actually).
The first monks were not Christians but Buddhists, starting about 500 BC. Probably the first Christian monks, in Egypt in the 300s AD, got the idea from Buddhist monks in India; there were plenty of traders traveling between India and Egypt during the Roman Empire.
To show that they were monks, Christian men had the back of their heads shaved bald. They called this being "tonsured" (TON-soord).
About some modern monks in the north of Scotland
Christian monks lived together in a monastery (MAHN-ah-sterr-ee) under the rule of an abbot (AA-but). They prayed five times a day, and went to Mass every day. Sometimes the monks sang in choirs. In between some of the monks copied manuscripts in the monastery's library, or taught other little boys to read and write, or did the laundry for the monastery. Other monks worked in the fields like most other people, planting grain for the monastery and harvesting it, and taking care of the monastery's pigs and sheep and cattle.
In some monasteries, the monks made wine to drink and to sell in town. Monks never married and were not supposed to have children, and they did not own any property of their own.
Sometimes men joined monasteries when they were older, either because they felt drawn to a religious life, like Gregory the Great, or as part of the life of a scientist, like Roger Bacon, or because they were so poor or sick that they wanted someone to take care of them. (For another reason, check out the story of Heloise and Abelard).
Even kings and emperors, like Michael V, sometimes became monks if they were deposed by a stronger rival who made himself king. Families sometimes also sent their boys to be monks if they had too many children and didn't want to have to split their farm among too many children for the inheritance. Girls couldn't become monks, but they could become Christian nuns.
Learn by doing: visit a monastery if there's one near you
More about Christian nuns
More about the Franciscans