In the catechism…
1494 The confessor proposes the performance of certain acts of
“satisfaction” or “penance” to be performed by the penitent in order to repair the harm caused by sin and to re-establish habits befitting a disciple of Christ.
scborromeo.org/ccc/para/1494.htm
This is a better explanation. Except it doesn’t express to whom the harm is done… which must be to us.
However elsewhere it goes to talk about God needing to be satisfied
616 It is love “to the end” that confers on Christ’s sacrifice its value as
redemption and reparation, as atonement and satisfaction. He knew and loved
us all when he offered his life. Now “the love of Christ controls us,
because we are convinced that one has died for all; therefore all have
died.” No man, not even the holiest, was ever able to take on himself the
sins of all men and offer himself as a sacrifice for all. The existence in
Christ of the divine person of the Son, who at once surpasses and embraces
all human persons, and constitutes himself as the Head of all mankind,
makes possible his redemptive sacrifice for all.
scborromeo.org/ccc/para/616.htm