The Sacrament of Reconciliation is one of the 2 Sacraments of Healing.
All of us sin. Sin is the absence of God's love and it breaks our relationship with God.
Christ gave his apostles the power to forgive sins and also the authority to reconcile sinners with the Church, "Receive the Holy Spirit. If you forgive the sins of any, they are forgiven; if you retain the sins of any, they are retained." (John 20:19,22-23)
Reconciliation restores us to God's grace and joins us back in an intimate relationship with God. It also reconciles us with the Body of Christ because whatever actions we do to hurt others, hurt God and the Church.
Although Baptism gives us a new life in Christ and washes away original sin, we are still inclined to sin because of our human weakness. Thus there is the necessity to always return to God and ask for his forgiveness and mercy like the Prodigal Son.
The graces (supernatural gifts) of Reconciliation are 1) reconciliation with God, 2) reconciliation with the Church, 3) remission of eternal punishment incurred by mortal sins, 3) remission of temporal punishments resulting from sin, 4) peace and serenity of conscience and spiritual consolation, and 5) an increase of spiritual strength.
The matter (visible signs) are: the acts of
man - contrition (to be truly sorry for one's sins), confession
(confessing the sins) and penance (to right the wrong).
The form (words) are: the priest's absolution, through the power of Jesus Christ, "God the Father of mercies, through the mercy and resurrection of his Son has reconciled the world to himself and sent the Holy Spirit among us for the forgiveness of sins; through the ministry of the Church may God give you pardon and peace, and I absolve you from your sins in the name of the Father, and of the Son, and of the Holy Spirit."