…on each of your sacrifices, you must offer salt. (Leviticus 2:13)
Both animal sacrifices and flour offerings had to be salted. An animal sacrifice was salted all over in the same manner as meat is salted as part of the kosherizing process. The salt was provided by the Temple from communal funds. The salt was applied to the offering in three locations during the sacrifice procedure.
The rationale for this mitzvah was discussed in its reciprocal mitzvah, #118. We salt sacrifices to make them more prestigious and desirable.
As with the previous mitzvah, this obligation applied to male kohanim in Temple times. It is likewise discussed in the Talmudic tractate of Menachos (20a-21b) and codified in the Mishneh Torah in the fifth chapter of Hilchos Issurei HaMizbe’ach. It is #62 of the 248 positive mitzvos in the Rambam’s Sefer HaMitzvos.