This is an important question. You will know that you have begun to forgive when you wish the other person well. This wishing-the-other-well may start as just a glimmer in your heart at first, but then it grows.
Anger is usually the place where forgiveness begins because when we forgive, we react to unfair treatment and our first reaction is likely to be anger or numbness, just as you describe. So, you are not alone in these feelings.
When you start a forgiveness process, please be aware that you are giving mercy to the one who hurt you. You are willing to get rid of resentment and to offer goodness of some kind to him or her. This takes time, so please be gentle with yourself.
As you continue to forgive, this idea of merciful goodness toward the one who was unfair builds and gives you a sense of hope and well-being. These feelings can be strong motivators to continue to forgive.
Do you have some sense of what forgiveness feels like? Please write again if you need more clarification.