As a whole, the Levites became responsible for "the service of the work of the Tent of Meeting", the Tabernacle (Numbers 4:3). The Hebrew word translated service also means warfare. Therefore their service in the Tabernacle was a figure of spiritual warfare; as at the golden calf incident (Exodus 32), the Levites were on the Lord's side.
Levi had had three sons: Gershon, Kohath and Merari. The Levites' work was partitioned according to their families:
the family of Gershon were responsible for carrying and setting up the curtains of the Outer Court, the Coverings of the Tabernacle, the curtain Door to the Sanctuary, the curtain Door to the Outer Court, together with all the ropes and fixings required for securing these curtains (Numbers 3:25-26)
the family of Merari were responsible for carrying and setting up the Boards, the Bars and the Pillars and Sockets of the Outer Court (Numbers 3:36-37)
the family of Kohath were responsible for carrying and placing the Ark of the Covenant, the Veil, the Golden Incense Altar, the Lampstand, the Showbread Table, the Laver and the Burnt Offering Altar, together with all the utensils these required (Numbers 3:31).
The children of Israel knew when it was time to move on in their journey through the wilderness, because the pillar of cloud (by day) or fire (by night) would move as a signal leading them. The Levites would dismantle the Tabernacle, carry it to the destination (determined by the pillar of cloud/fire) and then reassemble it at the new location.
When the Tabernacle was reared up at a new location, God commanded that the tribes settled around it in a specific order (Numbers 2:1-34):
on the East side: Judah, Issachar and ZebulunThe Levites were to encamp all the way around the Tabernacle (Numbers 1:53).
on the South side: Reuben, Simeon and Gad
on the West side: Ephraim and Manasseh (the sons of Joseph) and Benjamin
on the North side: Dan, Asher and Naphtali.