The covenant was accepted by Israel in Exodus 24:3 when they said,
“Everything the Lord has said we will do.”
Then that night Moses wrote down the words of the covenant the Lord had spoken (most likely the words of Exodus 21:1-23:19).
The next morning an altar was built at the base of the mountain, twelve stones representing the twelve tribes of Israel that had accepted the covenant were set up and both burnt offerings (completely consumed) and fellowship offerings (meat would have been cooked and eaten) were made. The covenant was read to the people and they again replied,
“We will do everything the Lord has said; we will obey.” – Exodus 24:7
Moses, Aaron, Nadab and Abihu and the seventy elders of Israel went up the mountain for the sharing of the covenant meal with the Lord. On the mountain they saw a theophany (an appearance of the Son of God) and they ate and drank with the Lord who had delivered them out of Egypt in fulfillment of his promise and in agreement with his covenant with Abraham. The food they ate may have included the meat of the fellowship offerings they had just made.
The theophany that they saw was similar to what Isaiah (Isaiah 6), Ezekiel (Ezekiel 1) and John (Revelation 1) saw. In verse 24:10 “they saw God,” but by 24:11 their seeing is a beholding or a gazing as they perceive the splendor in solemn silence, mesmerized at the view of the Divine Presence.
They ate the meal and confirmed the Mosaic Covenant with the Lord, the God of Abraham, Isaac, and Jacob.