After leaving Elim, the Hebrews had to traverse the wilderness of Sin on the way to Mount Sinai. Sin was a desolate wasteland, and the people got really sick of trudging across it on bare rations, so they began complaining about the trip, about being hungry, about how huge of a stupid dick Moses was, and how much better it had been in Egypt.
Moses started getting worried that people might attack him, so to pacify everyone, God told Moses that he was going to make it rain bread, but that there were certain rules everyone would have to follow….
So Moses told Aaron to tell everyone that God had heard their bitching and It was going to make it rain a bread called manna that looked like white coriander seeds, but tasted like honeyed wafers. That this manna would appear everyone morning, and that people should only gather enough for their families to eat for a single day, except on the sixth day, when they were to gather enough for two days. It was really, really important to only gather enough for a single day, because leftovers would rot, except on Friday nights. Furthermore, that evening, just to reward everyone, God would send a flock of quail to the camp so everyone could feast on meat.
That night everyone feasted on quail, and then the next day, sure enough the ground was covered in this white stuff that tasted pretty good. Everyone rushed out and scooped up bowlfuls of it. Most people followed Moses’s orders about how much to take, but those who didn’t and took too much found it crawling with maggots and stinking the next morning. As a result, when the sixth day came, people were pretty trepidatious about gathering double the amount, but Moses assured them that it wouldn’t rot because God. He also reminded them that God didn’t like it if anyone worked or did anything at all on the seventh day, so really, everyone should just stay home in their tents.
However, the morning of the seventh day, a lot of people still went out to gather the expected manna, but lo! there was none on the ground. When they went to complain to Moses he was all, duh. That’s why I told you to gather double yesterday. Are you stupid?
So the Hebrews ate manna every day for the forty years they wandered around the desert looking for Canaan. They also kept a jar full of it as a relic to commemorate their journey.