I'm a mother of a 8yr old son, I would like to know how can I received full custody of my son and what forms do I need to fill out.

Married to father, father on the birth certificate?

And full custody?
Legal custody, or physcial custody, they are different

But you basically go to court, do normally a parenting plan, and file for the level of custody you want.

The other side replys and files for the custody they want and if you can not agree, both of you fight it out in court