# He must go out to the altar that is before Yahweh

This is the altar of sacrifice just inside the courtyard of the tabernacle.

# make atonement for it

Like the holy place and tent of meeting, the altar is unclean because of the sins of the people.

# horns of the altar

"the projections at the corners of the altar." This refers to the corners of the altar. They are shaped like the horns of an ox.