John Gill Commentary Exodus 29:12

"And thou shalt take of the blood of the bullock, and put it upon the horns of the altar with thy finger; and thou shalt pour out all the blood at the base of the altar." — Exodus 29:12 (ASV)

And you shall take the blood of the bullock
Being slain, and its blood received into a basin:

and put it upon the horns of the altar with your finger ;
not sprinkle it with hyssop, as was done in some cases, but put on with the finger dipped into the blood in the basin; as the horns of the altar were the place where the sacrifice was bound, as some think, or however where persons in distress fled for refuge, and laid hold on, it may figure the blood of Christ, being effectual to the cleansing of their souls, and the remission of their sins, through the application of it to them by the Spirit of God:

and pour all the blood beside at the bottom of the altar ;
the rest of the blood not put upon the horns of the altar, all that was left of it. Jarchi says, there was a receptacle (for it) that protruded from around the altar, about a cubit from the ground; and here it was that the blood was poured.