You usually use the auxiliar verb + the past participle (passato prossimo) to describe an action which isn't over yet or which has just been completed. You can compare it to the present perfect. Example: I have just finished my homework. Ho appena finito i miei compiti. This is the grammar rule you should follow. However, in the common language and especially in the north of Italy, the passato prossimo is used to describe an action which is already over and it came to replace the simple past (passato remoto). Example: Yesterday, I went to a restaurant with my girlfriend. Ieri, sono andato al ristorante con la mia ragazza. It is commonly accepted, but still not properly used, even though using the simple past will sound weird to a lot of people.