The Sacrament of Penance and Reconciliation Uof is performed by both the confessor (priest), who is in persona Christie (person of Christ) and the penitent or person confessing their sins. This is the matter of the Sacrament.
The form of the Sacrament takes place with the (don't quote me on terms here) the intro or initiation where the penitent starts, “Bless me father for I have sinned…” Then they go on to state the time between this and their previous confession. The confessor or priest goes on to read a passage of Scripture in some cases or allow the penitent to state their sins.
Once completed, the penitent may state likely states that they're sorry for committing those sins and the confessor offers some words of encouragement and advice.
From there the penitent is instructed to make their Act of Contrition and once completed the confessor will typically absolve in the Name of Christ and provide a penitential act which completes the Sacrament and restores the saving grace of Christ in the penitent.
A good thing is to do an examination of conscience prior to confession (sin committed vis-a-vis the 10 Commandments). Also, provide number of sins and be exact as possible but you don't have to give the gory details.
Also, bear in mind that if a penitent knowingly decides the priest, hides something or is not truly contrite – perfect or not – their confession is invalid despite receiving a solution from the priest. This is because the only person who can forgive mortal sin is Our Blessed Lord Jesus.