Moses led Israel from the Red Sea on to the Wilderness of Shur. They traveled for three days through the wilderness without finding any water.
They got to Marah, but they couldn't drink the water at Marah; it was bitter. That's why they called the place Marah (Bitter).
And the people complained to Moses, "So what are we supposed to drink?"
So Moses cried out in prayer to God. God pointed him to a stick of wood. Moses threw it into the water and the water turned sweet.
That's the place where God set up rules and procedures; that's where he started testing them. God said, "If you listen, listen obediently to how God tells you to live in his presence, obeying his commandments and keeping all his laws, then I won't strike you with all the diseases that I inflicted on the Egyptians; I am God your healer."
They came to Elim where there were twelve springs of water and seventy palm trees. They set up camp there by the water.