Charles Ellicott Commentary Leviticus 9:5

"And they brought that which Moses commanded before the tent of meeting: and all the congregation drew near and stood before Jehovah." — Leviticus 9:5 (ASV)

And they brought. — That is, Aaron and his sons, according to the command of Moses, and the elders on behalf of the people, and according to the order of Aaron, who was directed by Moses to do so, brought the previously mentioned sacrifices.

And all the congregation ... — That is, the elders who represented the people, whom Moses summoned , and as many of the people as could find room assembled before the sanctuary in the courtyard to witness the newly-installed priests officiating for the first time.