I missed that question on the test" is different from "I'm so angry at my friend because she betrayed me."
Because we're all unique, each of us deals with our anger on our own terms. Sometimes we express it in a way that feels good in the moment, but causes more problems afterwards. Sometimes we keep our anger inside because we don't want to make trouble-but that just seems to make us feel worse.
As you can probably tell from looking at the adults in your life, everyone struggles with how and when to express anger. But anger isn't something we should ignore or avoid. In fact, when we get to know our anger -- what causes it, how we react to it -- and then learn how to manage it, it's a chance to get to know ourselves a little better and improve our relationships with other people.