The sixth aliyah begins with an inverted Hebrew letter "nun", then the words "Vay'hi binsoah ha-aron..." which is what the congregation recites as we take out the Torah in the synagogue, then another inverted "nun". The inverted nuns are actually written in the Torah. Rashi says that the inverted nuns show that the verse "Vay'hi binsoah..." is out of place, and only placed here to separate two sins. The first is that the Jews hurried away from Mount Sinai and what would be next to it is the Jews' complaining about conditions in the desert. After that is yet a third sin, murmuring for meat. In Judaism three things in a row make a "chazukah" (a permanent situation, in this case possibly designating the Jews to be permanent sinners). To avoid this three-in-a-row situation, the three are broken up by this nun- delineated passage.
This "nun" delineated passage is such a strong division in the Torah, that some commentators consider the Torah to have seven books instead of five. They are 1) Braishis, 2) Shmos, 3) Vayikra, ) Bamidbar up till Vay'hi binsoah, ) Vay'hi binsoah, ) The balance of Bamidbar after Vay'hi binsoah, and ) Devarim.
So, as we have said, here the Jews are three days away from entering the land of Israel, and now they start complaining about the manna and wishing for the food they were used to in Egypt. G-d promises to give them meat enough for a whole month, until they get sick of it. Moshe asks G-d for help with the people, so G-d appoints seventy elders to share the burden of leading the people with Moshe.