Islam is a monothestic religion based on the worship of Allah (Arabic for, simply, "God") as revealed by the teachings of the 6th Century prophet Mohammed. The writings of Mohammed were collected in the Qu'ran (alternatively spelled Koran) and form the basis of this faith.
In period, Muslims were regarded as the enemies of Christian Europe, and reviled accordingly. European period sources include all sorts of slanders and inaccuracies about Islam, including the accusation that they worshipped a variety of idols and devils. Curiously, one of the most feared Muslims, Saladin, was sometimes compared to the Nine Worthies, an example of chivalric virtue.
One major conflict between Christendom and the Muslim world was the Moorish Invasion of the Spanish peninsula. Another major series of conflicts were the Crusades in the Middle East, a chain vicious wars, primarily against Muslims, to "liberate" the city of Jerusalem and the Holy Land from Muslim control. Between Crusades, the lands of Outremer and the Crusader States held an uneasy peace with their Islamic neighbours.
The conflict between Christian and Muslim was somewhat ironic, because during and between each crusade Muslim influence on European culture became more and more widespread. One pertinent example is that Europeans use arabic numerals rather than roman numerals for mathematics.
Quite likely if you have a Middle Eastern or North African persona. Contact between Christian Europe and the Muslim Middle East was extensive, owing to the Crusades, the Christian practice of pilgrimage, and trade.