Anger is a normal human emotion and is only problematic if we choose to express it in unhealthy or maladaptive ways. The evolutionary function of Anger and the expression of aggression includes self protection from threats to our survival or the survival of our loved ones. Apart from this, there is no socially appropriate context for aggressive behaviour - although we may often feel angry.
A lot of chemical changes happen within the body when you experience anger (eg. the release of adrenaline and noradrenaline) and we now know with advances in neuroscience through the use of brain imaging that there are also structures in the brain, such as the Amygdala that short circuits information that usually would go to our frontal cortex to interpret the threat. This short circuiting helps us to act fast if our lives are in danger and we need protect ourselves, but it also prevents us from using effective judgement when we are under threat or some type of perceived threat. This is why you can go from 0 to100 in 1 second when you are angry and do or say things that you may regret later on.
People who use aggression to express anger also have the tendency to perceive that they are facing a more intense threat than there actually is which is generally seen as paranoia, over-reacting or acting out of character in some circumstances. Treatments for Anger involve relaxation (including mindfulness strategies), stress management, building assertiveness, increasing self esteem, helping a person to build more secure attachments to loved ones, learning to build empathy for others, and other strategies from Cognitive Behaviour Therapy, Acceptance and Commitment Therapy, Interpersonal Therapy, and Dialectical Behaviour Therapy approaches for mood regulation and learning how to think first and express feelings second. The most important facet of managing anger is the practice of self responsibility and aligning oneself with deeper values. Increasing tolerance and an increased acceptance of others is paramount to change in this area.