It is difficult to make generalizations about Buddhist communities' structure. The main institution is the Monastery  but its organizational structures vary from region to region and sect to sect. Some are strictly hierarchical; others are run like a family business. Some have central governing bodies; others do not. In fact in Buddhism the ultimate sources of authority are quite general. They are called the "Three Jewels".

Acknowledged authority: The Sangha, the Dharma and the Buddha

In Buddhism the ultimate sources of authority are quite general. They are called the "Three Jewels" on which every follower must vows adherence. These are:

• The Buddha: Depending on the various interpretation, it can mean the Historical Buddha (Siddharta), a Supramundane Buddha, or the Buddha Nature — the ideal or highest spiritual potential that exists within all beings.
• The Dharma: The teachings of the Buddha, the path to Enlightenment. Also in this case, it depends on which Sutras are considered as the most faithful teachings.
• Sangha: The community of those who have attained enlightenment, who may help a practicing Buddhist to do the same. Also used more broadly to refer to the community of practicing Buddhists, or the community of Buddhist monks and nuns.

Religious Institution: The development of Monasteries and their role in society

Originally the Sangha was a term describing the community of monks. The first Buddhist texts seem to suggest that a vision for society was not part of the Buddha's original plan. The Buddha had been seeking a path to enlightenment and escape from Samsara, and his focus was on sharing his insights with the renunciants who followed him.

As Buddhism shifted from groups of wandering ascetics to organizations with stable  structures, it was always connected to the communities within which these structures were built: the Monastery. As Buddhism was established throughout Asia, the Monastery became the fundamental institutional structure through which the various Buddhist teaching were transmitted.

Although Buddhism was initially disruptive to social structures by drawing men away from their social obligations, it soon became a productive contributor to local communities. A Buddhist Monastery provided its community with spiritual guidance and means of earning good Karman. Buddhism became known as a source of practical benefits for its followers. This practice grew from the worship the Bodhisattvas, compassionate enlightened beings who provided spiritual rescue but were also said to be able to protect people from dangers such as fires or floods. One might visit a Monastery to ask for healing or a myriad other things that would benefit one's life. Monasteries sometimes served as inns, offering beds and meals for travelers. Some provided social services such as schools or health care facilities.
As Buddhism spread and expanded, many Asian rulers welcomed the Buddhist organizations because they encouraged people to maintain strict moral Precepts (see below). The first and foremost example is King Ashoka (304–232 BCE) who sponsored Buddhism throughout all India. Rulers received the advantage of a well-behaved populace and Monasteries received financial support and official recognition.
In some countries, during some eras, Buddhism was an official state religion, and in those situations Buddhist Monasteries conducted rituals on behalf of the state, called on the powers of protective deities, and offered prayers to repel invaders in times of war. Buddhist Monasteries were also sometimes centers of rebellion, leading people who revolted against unfair rulers or poor social conditions.

Main Doctrinal Tenets: precepts for lay people and for monks

Essentially, according to Buddhist teachings, the ethical and moral principles are governed by examining whether a certain action is likely to be harmful to one's self or to others. Moral conduct for Buddhists differs according to whether it applies to the laity or to the clergy. A lay Buddhist should cultivate good conduct by training in what are known as the "Five Precepts". The five precepts are:

1. to avoid taking the life of beings;
2. to avoid taking things not given;
3. to avoid sexual misconduct; 4. refrain from false speech;
5. to abstain from substances which cause intoxication and  carelessness.
These are the basic precepts expected as a daily training of any lay Buddhist. On special holy days, many Buddhists, especially those following the Theravada tradition, would observe three additional precepts:
6. To abstain from taking food at inappropriate times.
7. To abstain from dancing, singing, music and entertainments.
8. To refrain from the use of perfumes, ornaments and other items used to adorn or beautify the person.

These last three are those regularly adopted by members of the monk's community. These three precepts refer to the ideal of poverty that should inform the monks' community. In addition to these eight precepts, the Buddhist clergy are governed by approximately 250 rules for male monks  and 350 rules for female monks. Four actions will result in expulsion from the Monastery: murder, stealing, sexual intercourse, and lying about spiritual attainments. Other infractions require some kind of punishment and also must be confessed to the assembled monks.

Sources’ comment

Source 1

Here the novice has just put on the monk's robe and  recites his vows to take refuge in the Three Jewels (see above). The rite of ordination may vary, but usually include the aforementioned vows, the vows to respect the Eight (sometimes ten) Precepts (see above) and the tonsure. This sanctions the novice’s commitment to leave the world and to exclusively seek enlightenment. In this case the rite is done in Pali, the language of the Theravada Buddhist canon, everything is repeated three times, to make sure that the candidate is firm in his mind.

For the lay person, it suffice to recite the vows of the Three Jewels  and adherence to the Five Precepts to be considered lay Buddhist.

Source 2

Today's Buddhist Monasteries (see above) come in many shapes and sizes. They may belong to families, neighborhoods, villages, cities, or nations. This fact highlights the diversity within Buddhism also in terms of organization. The Monasteries provide many of the same services and opportunities, both sacred and secular, that monasteries have offered historically. The Buddhist monasteries are a complex of buildings, statues, open landscapes, and ritual spaces. It is often the social center of a community.

Source 3

Buddhaṃ saraṇaṃ gacchāmi

Dhammaṃ saraṇaṃ gacchāmi

Saṃghaṃ saraṇaṃ gacchāmi

Dutiyam pi (repetition of above)

Tatiyam pi (repetition of above)

Translation:

To the Buddha I go for Refuge.

To the Dharma I go for Refuge.

To the Sangha I go for Refuge.

For the second time, …

For the third time, …

Pāṇātipātā veramaṇī sikkhāpadaṃ samādiyāmi.

Adinnādānā veramaṇī sikkhāpadaṃ samādiyāmi.

Kāmesu micchācārā veramaṇī sikkhāpadaṃ samādiyāmi.

Musāvādā veramaṇī sikkhāpadaṃ samādiyāmi.

Surāmerayamajjapamādaṭṭhānā veramaṇī sikkhāpadaṃ samādiyāmi.

Trans:

I undertake the training-rule to abstain from killing living creatures…

                   //                                   from taking what is not given

                   //                                   from wrong conduct in sexual desires

                   //                                   from false speech

                //                                 from intoxicants (such as those) distilled and fermented causing carelessness.

Links to other modules:

Christianity II. Themes, sec. 1,6 and 8
Hinduism sec. 11
Judaism I. History, sec. 1 and 2
Judaism II. Themes sec. 2.