The Lord said to Moses, "Cut for yourself two tablets of stone like the first, and I will write on the tablets the words that were on the first tablets, which you broke." - Exodus 34:1
God was really angry with the Israelites. So was Moses. After God miraculously freed his people from slavery in Egypt, the Israelites responded by complaining. Endlessly. Some even said that they longed to go back to Egypt because, while they were slaves there, the food was really top-notch. When they reached Mount Sinai, and Moses went up on the mountain to talk to God, the Israelites decided to make a new god to take the place of the one who hadn't done much for them lately.
God gave the Law to Moses, including "two tablets of the testimony, tablets of stone, written with the finger of God" (31:18). Then God told Moses that the Israelites had corrupted themselves by worshiping a golden calf and needed to feel God's wrath. Moses begged God to reconsider and God agreed. But when Moses saw for himself what was going on in the camp, "his anger burned hot"(32:19). He burned the calf, ground it to powder, put the powder in water, and made the people drink it. Moses commanded the sons of Levi to kill anyone who was not on God's side, and 3,000 men died.
But first Moses broke the stone tablets--the ones written with the finger of God. Anger can make you do things that you regret, and anger can lead to sin. But anger is not bad, in and of itself. Even Jesus got angry. In Ephesians 4:26, Paul writes, "Be angry and do not sin; do not let the sun go down on your anger." The first two words are a command: Be angry! Just don't sin in your anger.
God didn't want Moses to break the tablets. But God understood why Moses was angry. So God made Moses and the people of Israel new tablets. When you sin in anger, repent. God will take care of the rest.
Think about the last few times you got angry. Was it because of something that would make God angry? If not, then why were you angry?