God tells Moses that each day, he will give the Israelites food, but that they can't take more than their fill for one day. Every sixth day, he will give them twice as much food, so that on the seventh day (the Sabbath), he can take a break.
Moses and Aaron announce this to the people, and just like that, a bunch of quail show up in the camp as meat.
Then, some weird stuff, "on the surface of the wilderness, a fine flaky substance, as fine as frost on the ground," rains down (16:14). Everyone wonders what it is, but they eat it anyway. Hey, they were hungry.
The Israelites call the food "Manna," and describe it as "like coriander seed, white, and with the taste of wafers made with honey" (16:31).
The Israelites have trouble following God's instructions to finish all the manna each day; and when they try to save it, it gets all nasty with worms. Yum.
When they save it on the sixth day, it keeps for the next day, but some people go out on the seventh day looking for it anyway, even though God said it was a day of rest.
God gets annoyed. Duh.
Moses and Aaron save some of this stuff and eat it for forty years in the desert. Yep—forty years.