Why did they complain in the desert? Why wouldn’t they trust in God?

Sin makes us constantly rebel. Sin made them think that they could live their lives on their own accord, without God.

Why did Aaron and his sister oppose Moses?

Miriam and Aaron opposed Moses because of jealousy. They were wondering why God only spoke to Moses, why they couldn’t be in charge. They wanted something better, what Moses had. They weren’t content with what God gave them.

We have read about the cities of refuge before (Numbers 35). What were these cities for and how do they point us to Jesus?

If you accidentally killed someone, then the brother or close relative of the person you killed would be an avenger of blood and would go after you and try to kill you. You would have to go to a city of refuge in order to be safe from the avenger. In order to leave the city of refuge a high priest would have to die. Similarly, Jesus is our great high priest who died for us so we can get out of our city of refuge and not have guilt and shame.