It would vary depending on which order you were in (they all had their individual customs, and some were stricter than others), what kind of convent you were in (a rich one for the daughters of the nobility, or a very poor one, urban or rural) and your rank in the sisterhood, so I'll have to generalise greatly.

As a nun, your life would be governed by the performance of the Divine Office, a series of church services at regular intervals starting in the middle of the night and running until dusk (exact timings varied by the time of year). Attending these services in the convent church and taking part in group prayer and singing would be your prime duty as a nun, to assure that praise of God was never ceasing. At times of special significance such as Christmas, Lent, Easter and other church festivals there would be even more and longer services than usual, as well as processions and other ceremonies.

Every morning, after Mass, a meeting was held called the chapter, in a special room called the chapter house. There a chapter of the governing rule of the order would be read (hence the name), business would be discussed, jobs assigned and discipline carried out. Periods of study, reading and work, sometimes manual, sometimes not, followed, broken up by meals, usually two, more rarely three. The meals were taken communally in silence in the refectory, while listening to a reading of some improving book. Meat was generally banned from the monastic diet except for the sick, but by the 15th century this was not really adhered to, nuns would go to a separate dining room called a misericord to eat it. Food could be quite elaborate, depending on the wealth and strictness of the convent, and liberal rations of wine or beer were given.

There were a number of specialist ranks you could hold. The abbess or prioress (elected) was the boss and ran the show, they had great powers and ranked as a feudal lord (and often lived like one too, in a separate house attached to the convent). The cellarer was in charge of the food supplies and often administered the estates, the almoner gave aid to the poor, the novice mistress trained the young nuns, the infirmarer ran the on-site hospital, the treasurer managed the accounts, and many more. Those who held these jobs had various privileges.

In terms of material comfort the life led by individual nuns could be pretty nice. Even a poor convent offered facilities equal to a secular manor house, and the richest ones were palatial. By the 15th century the old custom of sharing a common dormitory had mostly been replaced by individual lodgings. These were often equipped with comfortable furnishings, the gifts of friends or relatives, and in some places could be rather luxurious. At rich aristocratic convents finely made versions of the monastic were common, and it was not unknown for nuns to follow secular fashions, frequently resulting in scandals. There were of course poor or strict convents where life was harsh and grim from choice or poverty.

It's important to remember that a great many nuns weren't there from religious vocation, they had been given to the Church as children or teenagers, been placed there by their families for social or political reasons or had joined to gain a secure life. Rich convents in particular were often dumping grounds for unwanted aristocratic women.

Hope this helps.