In the Sacrament of Reconciliation, Jesus the heavenly Physician heals us, through the instrument of his priest, of our sin which ruptures our relationship with God. Through the sacrament we are given special graces to resist sin in the future. In this sacrament we know our sins are forgiven because we have Jesus’ words backing it up: “If you forgive the sins of any, they are forgiven; if you retain the sins of any, they are retained” (Jn 21:21-23).
If it's been a long time since you last went to confession, have no fear. The priest will guide you. Below is the Rite of Penance which will walk you through the process. These brouchures are also available in the confessional.