I agree with north-malaysian that this is the practice of Catholics, not of all Christians.
I cannot find any Biblical reference which suggests that anybody
other than God can forgive sins.
It was one of the reasons why Jesus was seen to be blaspheming in the eyes of the scholars and teachers of the day: he was claiming to forgive people's sins - something only God was able to do!
Jesus sent out his disciples, and gave them the "power and authority to drive out all demons and to cure diseases, and he sent them out to preach the kingdom of God and to heal the sick" (Luke 9: 1-2) ... but he did not give them the power to forgive sins ...
It would be interesting to hear where this belief is coming from.
James talk about confessing our sins to each other and praying for each other:
Therefore confess your sins to each other and pray for each other so that you may be healed. The prayer of a righteous man is powerful and effective.(James 5:16)
But John makes it very clear that only God can forgive sins:
If we confess our sins,
he [in context: John is speaking about God] is faithful and just and will forgive us our sins and purify us from all unrighteousness. (1John 1:9)
Peace