How do i explain to a 3year old about his dad?

Repetition will help the name problem. He hears you call him "Bam," so that is what he calls him. Refer to your child's father as "your dad" or "your daddy." If you have a photograph of the father, put it in a frame someplace where your son will see it daily, and say to him, "say good morning to your Daddy, Sweetheart." And repeat at night, "say good-night to your daddy." Remind him that "Daddy" has been gone a long time and he is coming to see the boy soon. You want him to associate the face with the name and want him to be able to recognize the man.