Where do I start in adopting my wife's son.

He is three and always played an active roll in his life since he was born his biological father has refused contact since he was six weeks old

Hire an attorney, the attorney will fill out adoption paper work and paper work for the bio father to sign over his rights and permission from him for the adoption.

Then it is filed with the judge and that is about it.

Petition the Family Court in your county of residence. The biological father will have to sign a consent form if he can be located. If not then you'll need to demonstrate to the court that you made every good faith effort to locate him but without success.