The Tribe of Levi was a tribe of Israel- specially set apart by Yahweh for service to him and ministry of others. Being the intermediaries between God and Israel, Levites were responsible for all facets related to the Tabernacle (and later the Temple) and the functioning of Israel's theocracy (including enforcement of the Law alongside local elders). The most notable (but a minority) role a Levite could perform was that of Priest, which only was practiced by a descendant of Aaron. Other roles included: acting as musicians, maintaining the temple, guarding the temple or a host of other roles.
While the Patriarch Levi was a son of Jacob, Levi was not counted among the twelve tribes (instead Joseph was counted as Ephraim and Manasseh) and thus did not have a designated portion of the Promised Land. Instead, a tenth of the collective yields of Israel's crops and flocks would be provided them for food. In addition, forty-eight cities out of the other tribes' territory were given to Levi for agriculture, commerce, inhabitation and to give them a physical presence throughout Israel. Included in the forty-eight cities were six Cities of Refuge were accused of murderers could seek asylum from a family avenger and have trial.
Revenge against Shechem
The Tribe of Levi all descended from the patriarch Levi, the third son of Jacob and Leah. During Levi's adult life, his sister Dinah was raped by Prince Shechem of the Hivites. After this Shechem asked Jacob to have her hand in marriage. Levi and all of his brothers were furious, so they tricked the entire civilization to circumcise themselves. Levi and his brother Simeon were particularly angry. In vengeance, Levi and Simeon lead an armed force into the city and killed every male; also looting the entire city of its treasures. When Levi and Simeon were confronted by their father, they responded that Dinah should not have been treated like a prostitute.
Levi had three sons Gershon, Kohath and Merari. During his lifespan he and all of the Family of Israel took refuge in Egypt. At this time Levi only had his three sons with no other grandchildren. At the end of Jacob's lifespan in Goshen, Egypt he gave final words to all of his sons. While most of the sons received good blessings, Levi's family was given a curse: that they would be scattered and dispersed throughout Israel.
While in Egypt the Tribe of Levi began to grow. Each of Levi's three sons had their children. Each of these children became the progenitors of their respective clans, totaling to eleven clans. Amram, the head of his clan married Jochebed another Levite, and they bore Moses, Aaron and Miriam.