They said three things
From the humblest of mountains, Mount Sinai, Hashem chose to give us His Torah. He chose Moshe Rabbeinu who was the most humble man who ever lived. Only through such a man, could the chain of Torah be passed down to the Jewish people. The Ten Commandments are the beginning of the chain, followed by The Five Books of the Torah. Each world of the Torah was received by Moshe Rabbeinu and in exactly the same way was given over to Yehoshua, the next leader and prophet of Israel. Yehoshua faithfully gave it over word for word to the Elders and the Elders to the Prophets, until it reached the Men of the Great Assembly. Not only were the laws of the Torah handed down so carefully, but even Pirkei Avos - The Lessons of Good Behavior - were given over through this chain.