Where can I study about the priestly duties and responsibilities (old testament)?
The priestly (Kohen) duties and responsbilities began with Aaron and his sons (Exodus chapter 28 and chapter 29). The consecration of the Kohenim can be read in Leviticus chapter 8 and the priestly service can be read in Leviticus chapter 9. The appointment of the Levites and their Tabernacle/Temple duties is described in Numbers 3:5-13. The re-establishment of the Kohenim and Levites during the Second Temple period can be read in Ezra 6:15-22.