What were the priest's duties and the Levite's duties?
Under the Mosaical Law, the tribe of Levi was dedicated to the service of God. "At that time the LORD separated the tribe of Levi to bear the ark of the covenant of the LORD, to stand before the LORD to minister to Him and to bless in His name, to this day. Therefore Levi has no portion nor inheritance with his brethren; the LORD is his inheritance, just as the LORD your God promised him" (Deuteronomy 10:8-9). One member of that tribe, Aaron, was selected by God to be the High Priest. His sons and their descendants were to be the priests for the nation. As each High Priest died, another High Priest was selected from among the priests.
The priests served as the mediators between God and the people. They are the ones who took the people's sacrifices and offered them up to God (Leviticus 4:20, 26, 31; Hebrews 8:4). The High Priest, in particular, represented the whole nation of Israel before God (Exodus 28:12; Hebrews 5:1). When a priest sinned, he brought guilt not only upon himself, but also upon the whole people (Leviticus 4:3).
The priests also interceded on behalf of the people before God (Leviticus 9:22-24; Numbers 6:22-27). And they would inquire of God for the nation (Exodus 28:30).
The Levites, members of the same tribe, but who were not descendants of Aaron, served as aides to the priests, doing things like helping to prepare the sacrifices. They took care of the temple, making repairs when needed, and served as musicians, singers, doorkeepers. (Numbers 1:50-53; 3:6-9; 4:1-33; I Chronicles 23). Service began at the age of 25 (though later changed to 20 under King David) and continued until they reached the age of 50 (Numbers 8:24; I Chronicles 23:3,24-32). The Levites were also the teachers of Israel (Deuteronomy 24:8; 33:10; II Chronicles 35:3; Nehemiah 8:7) and the nation's scribes (II Chronicles 34:13). The Levites were also the nation's judges (Deuteronomy 17:8-9; 21:5; I Chronicles 23:4; II Chronicles 19:8; Ezekiel 44:15, 24). They were also the nation's regulators. For instance, they were responsible for accurate weights and measures used in Israel (I Chronicles 23:29; Leviticus 19:35-36).
Neither the priests or the Levites spent all their time of service at the temple. Most of the year they had their own homes, farms, and business of which to take care. According to a fixed schedule they took turns performing the duties assigned to them.