As in a court of law, confession means admitting that you’ve done something wrong, or that your values were leading you down the wrong path of conduct. When you “confess that Jesus is Lord,” you admit that you didn’t recognize Jesus’ authority and did not obey His commands.
Just as in court, confession is something you say out loud. You can confess sins to a mature Christian, a pastor, a counselor, or to God in prayer. Before you confess to a human being, make sure they have the training and credentials to deal with the issue you are confessing.
Many people stop at confession, but it is really the second step in a process. The first step compunction, the second step is confession, and the third step is repentance, which is a change in your values that leads to a change in your conduct. In other words, you feel bad about it, then you admit it, then you try very hard never do it again. The technical term for a person who skips the last step is “hypocrite.”
In the ancient church, catechumens were required to stand on a box in front of everyone and confess their sins to the the entire congregation. This eventually ran into practical problems, because a convert’s confession could implicate other people, especially if the convert were a government official. Since we are not supposed to confess other people’s sins, catechumens were given the option of confessing to a clergyman privately. Confessing to clergy began as an option in the fourth century, then gradually became the norm.
Today, confession is a church rite that some churches consider a sacrament. Confession to clergy is still the practice among Orthodox, Anglican, Lutheran, and Catholic Christians, though among Anglicans and Lutherans, it is optional.