The first major section of Leviticus explains the sacrificial system and the priesthood. There were sacrifices for atonement (whole burnt offering, sin offering, and guilt offering). And there were sacrifices for worship (grain offering and peace offering). Each sacrifice taught Israel about God's character in practice.
Priests led the sacrificial worship at the Tent of Meeting (the tabernacle). They taught the people about God's revelations to Moses at Sinai. They represented the people before God, especially on the Day of Atonement (chapter 16). Priests received a portion of the offerings for their support.