This lesson is about repentance from sin and the attitudes and actions that accompany it and make it genuine.
1. Godly sorrow
The scriptures tell us that "godly sorrow produces repentance" (2Co 7:10). Repentance requires that we feel remorse, and truly sorry for the sins we have done. Of course, we can have a sorrow for sin and still lack repentance. The rich man who "went away sorrowful" (Mtt 19:16-22) is an example. We may feel sorry about being condemned for sin, yet still not want to let that sin go. So there can be sorrow for sin without repentance, but there cannot be repentance without a genuine godly sorrow.
2. Guilty conscience
Peter's preaching caused many people to be "cut to the heart" and to cry out "What shall we do?" (Acts 2:37). Peter then told them to repent and be baptized (Acts 2:38). Their conviction of sin led them to repentance. Of course, one can have a guilty conscience without repentance. For example, Judas who betrayed Jesus had a guilty conscience, but he committed suicide instead of repenting unto life (Mtt 27:3-5). So there can be a guilty conscience without repentance, but there cannot be repentance without a genuine conviction of guilt.
3. Confessing sin
Not only should we feel the conviction of sin, but we should be willing to acknowledge the sin to God. Of course people can acknowledge sin without repentance. We have all heard people boast about their evil deeds. We also know that on Judgment Day every one must give account to God (Rom 14:10-12). In the case of those who have sinned and not been forgiven, their account to God must necessarily entail a confession of sin. However they will have no more opportunity to repent. So there can be a confession of sin without repentance, but there can be no repentance without confessing sin.