All religious communities of men and women must be authorized by the Church and cannot exist apart from such authorization. Each community follows a rule of life, and constitutions that implement the rule. Some approved rules are hundreds of years old and are very general in nature. The constitutions are updated periodically, help define the spirit and charism of the community, specify its organization and governance.
Some religious communities are contemplative. These groups separate themselves from the world in order to engage in a full time ministry of prayer and reflection, supplemented by work done internally within the cloister in order to support themselves. Examples of such communities are the Trappists (both monks and nuns), and Poor Clare and Discalced Carmelite nuns. Members of contemplative orders seldom leave their monastery, and they almost never engage in parish ministry. Some communities have strong contemplative traditions, but over the years have accepted some outside work, including parishes. This is particularly true outside of Europe. In the US, for example, Benedictine monks and nuns regularly work in parishes and other active ministries.
Other religious communities are active. Their rule and constitutions oblige them to work in the world. Many of these communities were founded to do some particular job, such as teaching, care of the sick, etc. For example, the Salesians of St. John Bosco were founded to work with poor and working class young men, and they staff orphanages and schools. Other active communities are more generalist in their approach, and their members take on a wide variety of tasks. Many communities of sisters that were originally founded for one particular work are now working in many areas of life.
A third type of religious community strives to live a mixed life. Their members work in active ministry, but also try to balance their activity with a strong contemplative focus. St. Thomas Aquinas called this the best and most difficult type of religious life. Examples of communities trying to live a mixed life are the Dominicans (St. Thomas Aquinas was a Dominican) and the Franciscans, including the Capuchins. Members of these communities work in many areas.
Many religious communities are worldwide (such as the Capuchins), and are organized into geographic units called provinces. Many other communities exist in only one country, or in even only a particular diocese.
Communities of men may consist of priests and lay (unordained) brothers. Some communities are nearly entirely lay (e.g. the Christian Brothers), and others have very few lay members (e.g. the Jesuits). The Capuchins consider themselves to be a community of brothers, many of whom are ordained.