It is normal to feel angry in our lives when we feel frustrated or when something does not happen as we wish or expect. However, if you usually feel excessive anger and you react in aggressive or violent ways to events or circumstances that are not expected for that reaction and it causes problems for yourself and to your interpersonal relationships; then, you could have anger issues.
When someone has anger issues, it is very usual that that person is covering important feelings of sadness, frustrations, and unmet emotional needs that she or he is projecting outside of them in violent or aggressive ways. The person is very sensitive to frustrations and reacts to them in an automatic way. The process of thoughts is not there, just pure negative emotions.
Therapy assists people to work on their emotional frustrations, on helping them think and express more about how they feel. This will allow the thought process to be more present in their behaviour, and not just the emotional reaction.