Both men and women could enter the convent during the Middle Ages. As I discussed in an earlier post on monasticism, male monasticism came first, and until the late Middle Ages there were more houses for monks than for nuns.
Yet there were also nunneries in the West from the sixth century onward. During the early medieval period, one would sometimes find double monasteries, with a house for men and a house for women next to each other. Such a double house would inevitably be ruled by a woman, an abbess, rather than a male abbot.
Because the medieval view of women was that they were equal to men in the eyes of God, it was considered appropriate for them too to enter the monastic life, even though rules for women were less harsh than those for men, in the assumption that women's weaker bodies could handle less rigor. On the other hand, their physical weakness was also considered a sign of spiritual strength, because they had more to overcome.
Due to the relative shortage of nunneries for much of the Middle Ages, women might be forced to set themselves up in little cells, perhaps next to a monastery, if they wanted to devote themselves to the religious life.
Whereas the majority of monks throughout the Middle Ages had entered the cloister as boys and grew up as monks, probably the majority of nuns, until the late Middle Ages, were adult converts. Certainly a young girl could go off and join the nuns, but they were outnumbered by women who had been widowed and decided that they had had enough of dealing with men. As well as widows, the adult converts included women whose husbands had decided to become monks--at least theoretically, if one spouse entered the cloister, both were supposed to. Such women, experienced in the affairs of the world and often having managed a castle, were considered appropriate choices as abbesses.
Nunneries, like monasteries, might run day schools, where girls from the region would go to get an education. These pupils might decide in their teens that they would like to become nuns, but most used their education in the secular world. By the late Middle Ages, cities would normally have at least one nunnery, providing both education and a home for religious women.
One of the challenges for a nunnery was dealing with laymen. The abbess would do so, although many of the nuns would never see a male again after taking their vows. Most nunneries would have men who could act as their representatives in secular affairs where a nun would be at a disadvantage. Another big challenge was the liturgy. Because women could not become priests, an abbess would have to have a priest under her direction to say Mass. The nuns, however, could and did sing the psalms, just as did monks.