Q: Why do Catholics confess to a priest?
A: Because it is a gift Jesus left for us. But to really understand how and why and where do priests get the authority to forgive sins, one must understand why Catholics follow the pope.
The following linked question explains why Catholics confess to a priest, and how can they forgive sins, transform bread & wine into the body & blood of Jesus…literally… etc. Why do Catholics follow the Pope?
“Always be prepared to make a defense to anyone who calls you to account for the hope that is in you”
1 Peter 3:15