Confess somebody = (of a priest) listen to somebody doing this.

• The priest confessed the criminal.

Confess to somebody= tell a priest what you have done so that you can be forgiven OR admit something to somebody.

• The criminal confessed to the priest that he had stolen the gold ornaments.

Related usages :

• She confessed to her mother that she had told a lie. (i.e admitted that…..)
• He has confessed to the priest that he murdered the neighbour.
• I must confess that the house extension is costing a lot more than I expected.
• It was all very confusing, I must confess.
• The priest is ready to hear confession in English.
• The accused made full confession during police interrogation.

Confessional : private place (stall) in a church where a priest sits to hear confessions.

Confessor : priest who has authority to hear confessions.