Anger is a completely normal, usually healthy, human emotion. But when it gets out of control and turns destructive, it can lead to problems at work, in your personal relationships and in the overall quality of your life. And it can make you feel as though you are at the mercy, even frightened of an unpredictable and powerful emotion.
If you feel that your anger is really out of control, if it is having an impact on your relationships and on important parts of your life, you might consider counselling to learn how to handle it better because often the triggers, such as a bad day at work, is not necessarily the symptom.
Anger possibly has built up over time, perhaps it has never been an acceptable emotion to express or when it is expressed it is raging and often filled with remorse and guilt after its expression. It is true that angry people need to learn to become assertive (rather than aggressive), but most books and courses on developing assertiveness are aimed at people who do not feel enough anger. These people are more passive and acquiescent than the average person; they tend to let others walk all over them. That is not something that most angry people do.
Anger cannot be eliminated and events and situations will always cause anger and sometimes it will be justifiable anger. Life is frustrating at times; it involves pain, loss and the unpredictable actions of others. You cannot change that, but you can change the way you let such events affect you and talking about what can be shameful feelings about having anger can be a very useful way of taking the sting out of it.