In the Middle Ages, churches were actually parishes, although the term "church" could also be applied to monasteries and abbeys. The chancel, which contained the altar, belonged to the lord of the manor. The nave and tower belonged to the people of the parish. The church tower doubled as the priest's residence and was built for defense. School was held in the church porch or a room above it. Often the church was built in the shape of a cross, however distorted, and that shape is still used today for modern churches.

For more information:

Medieval Churches and Monasteries in England
Design of Medieval Churches