Numbers 7-8

Offering of the Tribes
When the tabernacle was completely set up, Moses anointed and consecrated it. Then the leaders of all the tribes came forth to give their offerings. Carts and oxen were given to the Levites, Gershonites and Mararites to enable them to do their work. However, the Kohathites did not get anything because they had to carry the holy items on their shoulders. (!)

Then, the next 12 days, each of the tribes took turns bringing the same exact offering:

One silver plate weighing a hundred and thirty shekels, [a] and one silver sprinkling bowl weighing seventy shekels, [b] both according to the sanctuary shekel, each filled with fine flour mixed with oil as a grain offering; 14 one gold dish weighing ten shekels, [c] filled with incense; 15 one young bull, one ram and one male lamb a year old, for a burnt offering; 16 one male goat for a sin offering; 17 and two oxen, five rams, five male goats and five male lambs a year old, to be sacrificed as a fellowship offering.

Moses then entered the Tent of Meeting to speak with the Lord.

God told Moses to ask Aaron to set up the 7 lamps to light the area in front of the lampstand, which Aaron happily obliged.

Levites Are Important!
God again emphasizes and declares that the Levites are wholly His in exchange for all the firstborns in Israel. He has given the Levites to the Israelites to do the work at the Tent of Meeting on behalf of the Israelites so that they will not suffer plagues.

God instructed the Levites to remain ceremonially clean. Aaron would then present the Levites as a wave offering to the Lord.

Levites between the ages of 25-50 would work. After 50, they can help out, but are essentially retired.