The past participle ressembles to the participio passato. Unlike the present participle, which exists only in theory, but not in practice in Italian because the participio presente is not a productive system any more (it is not possible to form the participio presente of any verb) the participio passato can be formed from any verb and is used the same way as in English. It can be used as an adjective and corresponds to the passive voice. In most cases it is used to substitute a relative or a temporal clause.
The houses constructed in the sixties must be repaired.
The letters written by hand are nicer.
The whole thing is really easy once understood how it works.
Limit the quantity of cigarettes smoked during the day.