A father (also called Dad or Daddy) is a male parent of someone. Most human beings are born from a mother and a father. The father of a person's husband or wife is their father-in-law. Fathers determine the gender of their child through a sperm cell which either contains an X chromosome (female), or Y chromosome (male).
In some religions, such as the Jewish religion or Christianity, God is called Father. In the Christian belief God is three Persons; Father, Son and the Holy Spirit. Father can also be used as a title for a Catholic priest.
If a man and a woman get married, then in many Western countries, the woman and their children will use the man's last name. For example, if the woman is called Sasha Dooley and the man is called Ben Allen from birth, and they get married, then she will become Sasha Allen and the man will still be Ben Allen. They might have children named John Allen and Mary Allen.