Need advice on where to start on filing for custody of child?

I was in an abusive relationship from the age of 18-23. We had a child during that time. In the mist of things when my child was 5 I lost everything. No job no house no means to support him so I let him live with his father due to the fact he was in a better financial situation at the time. As time grew I now am in the position of being able to support my child with no help and I have a house,job and car. The child's father is being bitter and play little games of not letting me see him for long periods of time. This has been going on for years. I was very afraid of him. He beat my a** plenty of times. Now I've over come that and am a stronger person. He will not allow me to get my child full time even though my son wants to live with me. When he ask if he can live with me he gets a whooping. Where do I start?