Question: Why do we have to confess to a priest?

Answer:

Leviticus 19:20–22 tells us:

If a man lies carnally with a woman . . . they shall not be put to death. . . . But he shall bring a guilt offering for himself to the Lord . . . And the priest shall make atonement for him with the ram of the guilt offering before the Lord for his sin which he has committed; and the sin which he has committed shall be forgiven him.

Christ delegated authority to his New Testament ministers to act as mediators of reconciliation as well. Jesus made this clear in John 20:21–23

Jesus said to them again, "Peace be with you. As the Father has sent me, even so I send you." And when he had said this, he breathed on them, and said to them, "Receive the Holy Spirit. If you forgive the sins of any, they are forgiven; if you retain the sins of any, they are retained."

Christ sent the apostles and their successors to proclaim the gospel with his own authority (Matt. 28:18–20), to govern the Church in his stead (Luke 22:29–30), and to sanctify it through the sacraments, especially the Eucharist (John 6:54; 1 Cor. 11:24–29) and confession.

Much more information can be located here:

A Confession to Make

Confessing to a Priest

Confession by the Early Church Fathers

Forgiveness of Sins

Protestant Misconceptions about Confession

Question: Why do we call a priest "father"?

Answer:

Perhaps the most pointed New Testament reference to the theology of the spiritual fatherhood of priests is Paul’s statement, "I do not write this to make you ashamed, but to admonish you as my beloved children. For though you have countless guides in Christ, you do not have many fathers. For I became your father in Christ Jesus through the gospel" (1 Cor. 4:14–15).

Peter followed the same custom, referring to Mark as his son: "She who is at Babylon, who is likewise chosen, sends you greetings; and so does my son Mark" (1 Pet. 5:13). The apostles sometimes referred to entire churches under their care as their children. Paul writes, "Here for the third time I am ready to come to you. And I will not be a burden, for I seek not what is yours but you; for children ought not to lay up for their parents, but parents for their children" (2 Cor. 12:14); and, "My little children, with whom I am again in travail until Christ be formed in you!" (Gal. 4:19).

John said, "My little children, I am writing this to you so that you may not sin; but if any one does sin, we have an advocate with the Father, Jesus Christ the righteous" (1 John 2:1); "No greater joy can I have than this, to hear that my children follow the truth" (3 John 4). In fact, John also addresses men in his congregations as "fathers" (1 John 2:13–14).

By referring to these people as their spiritual sons and spiritual children, Peter, Paul, and John imply their own roles as spiritual fathers. Since the Bible frequently speaks of this spiritual fatherhood, we Catholics acknowledge it and follow the custom of the apostles by calling priests "father." Failure to acknowledge this is a failure to recognize and honor a great gift God has bestowed on the Church: the spiritual fatherhood of the priesthood.

Much more information can be located here:

Call No Man Father

Why do Catholics call the pope "Holy Father"?

Why do Catholics call priests "father" when Jesus said "call no man father"