A Jedi uses the Force for knowledge and defense. Never for attack.
Anger, fear, aggression... the Dark Side of the Force are they! Easily they flow... quick to aid in a fight.
You will know! When you are calm, at peace. Passive.
We all fall to the Dark Side from time to time. Yelling at those who we love. Giving that asshole the finger after he cuts you off. Taking a little extra for yourself, even though it's not yours. The failings of humanity.
This is the beauty of the story of Anakin Skywalker. He represents the worst in us all. He shows us the blood on our hands after we unleash our own inner Death Stars. He is fear and being afraid.
Even better, he is also the spark. The tiniest glimmer of light in the blackest dark. That seed of hope. There is still good in him...