It begins as a feeling of slight frustration. Maybe you'll growl or let out a few careless "fucks". Can be caused by slight things, like spilling your drink on your clothes. It's more of an annoyance scratching the inside of your skull, not anger.
The next level can be characterized with more magnitude than the first "stage" I described. You'll curse and put on a hostile facial expression. People may begin to notice.
The third stage is a more intense, and unrestained version of phase two. You'll clench your fists and yell. Adrenaline often will begin pumping, depending on your situation.
The last stage is what people refer to as rage. You lose control of yourself. Anything that comes in your way will often become a victim of a punch. In this stage, the conscious mind does not exist and cannot stop you from making choices, eg fighting. The most amazing feeling about this is the unrelenting strength that you receive from the pumping adrenaline.
Anger is truly an amazing and destructive emotion, it brings us closer to our true primal roots.