God said Gideon's army was too big since He wanted Israel to know that it was not the might of 32,000 men that saved Israel but God himself. He lowered it to 300 by taking away the people that wanted to go home and the ones that couldn't keep guard of their surroundings when they were drunk.
In Israel, God was angry with his people because of their sin such as worshiping false gods and punished them by leaving them in the hands of the destructive Midianites for seven years.
Gideon wants a sign that this is actually a true angel of the Lord. Gideon asks the angel to combust an offering of food. He believes that she is a true angel after she does what she asks.
God tells Gideon to destroy one of his fathers altars to a false idol named Baal and replace with an altar to God and make an animal sacrifice on it. He did this at night so he wouldn't be caught.
After the townspeople found out about what Gideon had done; they demanded for his execution. Gideon's father defended Gideon by saying that if Baal was truly a God, he would be able to defend himself.
Gideon calls to arms several people to fight against the Midianites and they join him. He asks God for a sign to show that He is with them and he does what he asks.