Anger is an emotional state that arises in response to perceived threat, injustice, or violation of something important. It is one of the most fundamentally useful emotions, and one of the most mismanaged.
Anger is information. It tells you that something matters to you and that something has gone wrong with it. A boundary was crossed. Something unfair happened. A need went unmet. You were treated as less than you are.
The problem with anger is rarely the emotion itself. It is what is done with it. Anger expressed destructively causes harm. Anger suppressed becomes resentment, depression, or a persistent low-grade hostility that makes no sense in context.
Learning to work with anger requires first tolerating its presence, not acting on it immediately, but not suppressing it either. Acknowledging it. Understanding what it is pointing at. Then deciding what, if anything, to do with that information.
The person who has learned that anger is not allowed develops other symptoms. Understanding the connection between those symptoms and the suppressed anger is often significant therapeutic work.