Unless you are writing a Mary Poppins story, anger is very likely going appear in your story. As the intent is for the reader to connect with the character, knowing about anger will help better craft the emotion.
What Is It?
Anger is a natural response to perceived or actual pain, 
grievance, conflict, injustice, negligence, humiliation, betrayal, frustration, being overwhelmed, feeling controlled, irrational beliefs, low self-esteem, insecurity, brooding about personal problems or any of the above, traumatic, or enraging event. Any or all of this is directed toward a specific person or group of persons — or at one’s self.
Physical Changes
Avoiding Freudian brain surgery, I’ll not get into what happens in the brain, but suffice it to say 
that the thinking process shifts from the thinking part to the emotion storehouse part, usually faster than a politician changes opinion based on public poles or a lightning strike, which ever occurs first. Other than that, not much else happens except adrenaline is dumped wholesale into the body, the heart rate increases, and blood pressure spikes.
Unlike the onset, return to the “resting state” is NOT fast once the target of anger or threat is no longer present. Something like cold molasses. Adrenaline doesn’t give up easily. Clearing that stuff out can take hours, even days, and if something happens in the meantime, anger is easier to re-ignite.
Effects / Results
Clenched jaw
Grinding teeth
Tensing body
Hot feeling in neck and face
Sweating, especially the palms
Shaking or trembling
Heart attack or stroke
High blood pressure
Headache
dizziness
Digestive problems / abdominal pain
Increased anxiety
Depression
Insomnia
Skin problems like eczema
Now, if some of these things sound familiar to what might result from FEAR, you’ve been there.
Expressioned
Usually, we think of anger occurring outward from the 
individual (conscious of the action.) Not always. Humans have the ability to turn such things inward and self-destruct (unconscious of imploding.) Some behaviors are:
Violent / destructive (ie. damaging one’s property, road rage)
Irritability
Assertive / non-aggressive
Irrational reaction to inconsequential things
Demanding immediate action
Impetuousness
Taking inappropriate action or risks
Suppression – When not allowed outward expression, it turns inward (the implosion effect) can result in:
a. Hypertension, high blood pressure, depression
b. Passive-aggressive behavior (avoiding a head-on confrontation, getting back indirectly
c. Perpetually cynical / hostile, putting others down, critical of everything
Blind to the truth / unable to accept what is sensible / correct
Less able to think and act rationally
Poor listening
Senses affected – do not work properly when in extreme anger
Jumping to conclusions
Often followed by depression
Clues
Back to You
There you have it in a (fairly large) nutshell. Instead of writing, “He is angry,” “She said with anger,” you can describe what the character is feeling, what others are seeing, hearing, and feeling, and the reader can relate on a personal level (unless they happen to be Mary Poppins.)
