Catholic Mass in Italy
While the word "catholic" means "universal" and in theory every Catholic church is the same, there are a few distinguishing features of Italian Catholicism:
Language - obviously one big difference is that most Italian church services are in Italian, although a handful of services (especially in Rome) are in Latin. Also see the Wikinapoli listing of English services in Naples. A few other places in Italy have English masses (there are more English services in non-Catholic churches):
Rome - St. Patrick's is the main English-language church for Americans, although there are also services at Santo Spirito in Sassia (the Pontifical North American College points out that their Sunday service is convenient to attending the Angelus with the Pope afterwards), and a few other places listed on Saints in Rome
Florence - Santi Apostoli has a few English services, and the Duomo (Santa Maria del Fiore) has a 5 PM Saturday vigil in English
Venice - San Zulian (San Salvatore parish) apparently has an English service most Sundays at 11:30 AM
Milan - Chiesa del Carmine has several English services ever week
Saints/Visceral - while the Catholic church in general recognizes a number of saints--holy men and women--in Italy the veneration of saints is more important than in the U.S. Italian Catholicism often is more physical, with relics and other sacred objects taking on a larger role.
Semi-Official/Cultural versus Religious - unlike the American constitutional separation of church and state, it is basically assumed that all Italians are Catholics...nevertheless, many of them do not regularly attend church services. You might say that most Italians are "culturally" Catholic even if they are not necessarily "religious" (in the American sense of going to church regularly).
Understanding Italian Mass
The following explains the general flow of the Italian Mass, such that also non-Catholics can have an idea about what's going on:
General Rule: Follow Along!
If the rest of the people stand up, you should stand up too, etc. To help with the language barrier, try printing out the words to the Mass and/or Readings before you go (see "Resources," below). One exception: generally speaking if you are not Roman Catholic it is asked that you not receive Communion (the bread and wine). A page written by American bishops goes into details.
Introductory Rites (Getting Started)
Often a bell will ring, and everybody stands up as the priest enters; there will sometimes be a song
Everyone makes the sign of the cross and says "Amen" (since it's based on Hebrew/Greek, it's the same word as in English! They of course pronounce it "AH-mehn" not "ay-MEHN"). A few other times in the mass, the priest will say "Preghiamo" (Let us pray), recite a prayer, and at the end the people respond: "Amen."
The priest asks that God's blessings be with the congregation, who respond "E con il tuo spirito" ("And with your spirit")
Penitential Rite (Saying Sorry): The priest and congregation pray for forgiveness for things they've done wrong, repeating Signore pietà and Cristo pietà ("Lord, have mercy" and "Christ, have mercy")
Gloria (Glory to God): everyone recites a rather long prayer, sometimes sung, praising God. For the full words and translation, see Resources, below.
Liturgy of the Word (Bible Reading)
Everyone sits down, and somebody reads the first reading, usually from the Old Testament (Hebrew Scriptures). At the end of the reading, the reader says "Parola di Dio" and the people respond "Rendiamo grazie a Dio" ("The Word of the Lord"/"We give thanks to God" or "Thanks be to God").
After the first reading is a "responsorial psalm" taken from the Book of Psalms: the congregation says/sings the refrain.
The second reading is usually from the Letters of Saint Paul. Same Parola di Dio/Rendiamo grazie a Dio at the end.
Everyone stands up to prepare for the Gospel reading; once again the priest asks the Lord to be with the people, who respond "E con il tuo spirito" (seeing the pattern now?). The priest will then announce which gospel the reading is from (Matteo, Marco, Luca, or Giovanni) and the people respond "Gloria a te, o Signore" (Glory to you, O Lord). You'll notice people making tiny crosses on their forehead, lips, and chest; this is a silent prayer that the words they are about to hear stay in their minds, on their lips, and in their hearts.
At the end of the Gospel, the priest will say "Parola del Signore" and everyone responds "Lode a te, o Cristo" ("Praise to you, Oh Christ") before sitting down.
The priest then gives a homily (discussion) about the readings and what they mean to the congregation.
Profession of Faith (or Creed): When the priest is done with his homily, everyone stands up and recites another long prayer summarizing their faith. For the full words and translation, see Resources, below. Just like in English services, there is a lot of mumbling!
Prayers of the Faithful: Various prayers for the community will then be offered up; everyone responds "Ascoltaci, o Signore" ("Hear us, o Lord").
Liturgy of the Eucharist (Getting Ready for/receiving Communion)
Presentation of the Gifts: there will sometimes be a song, and they'll pass around a basket for donations to pay for church activities and various charitable causes. Afterward, the priest presents the "gifts" of bread and then wine to God, and the people respond each time "Benedetto nei secoli il Signore" ("Blessed for centuries is the Lord"...or "Blessed be God forever"). At the end the priest and congregation pray that the gifts be acceptable to God (another somewhat long prayer, see Resources for more) and everybody stands.
Eucharistic Prayer: in the ritual where the bread and wine are transformed (according to Catholic faith) into Jesus's body and bood, we have some quick call and response, long prayers, the Sanctus ("Holy Holy", a prayer derived from the one the angels sang at Jesus' birth) after which everybody kneels, and some more long prayers. See the Resources for the full text.
Lord's Prayer: Everyone then recites together the Our Father: "Padre nostro, che sei nei cieli, sia santificato il tuo nome. Venga il tuo regno, sia fatta la tua volontà, come in cielo, così in terra. Dacci oggi il nostro pane quotidiano, e rimetti a noi i nostri debiti, come noi li rimettiamo ai nostri debitori, e non abbandonarci alla tentazione, ma liberaci dal male." The priest says a few words, then everyone adds, "Tuo è il regno, tua la potenza e la gloria nei secoli."
Kiss of Peace: The priest asks that the peace of the Lord be with the congregation (who respond, once again, with "E con il tuo spirito"). Everyone then shakes hands and/or kisses each other to express this sentiment; it is common to say "Pace" ("peace") or "Pace del Signore" ("The peace of the Lord") when you do this.
Fraction Rite/Agnus Dei: The priest will begin breaking up the hosts (the bread, or "fractioning" it) as everyone prays the "Agnus Dei" prayer addressed to the Lamb of God (i.e. referring to Jesus as a sacrificial lamb): "Agnello di Dio, che togl i peccati del mondo, abbi pietà di noi" ("Lamb of God, who takes away the sins of the word, have mercy on us") repeated twice, then the same thing but the last part being "dona a noi la pace" (give us peace). The priest then holds up the bread and wine and says "Ecco l'Angelo di Dio, che toglie i peccati del mondo" ("Here is the Lamb of God, who takes away the sin of the world") and the people respond: "O Signore, non sono degno di partecipare alla tua mensa, ma di'soltanto una parola e io sarò salvato." ("O Lord, I am not worthy to participate at your table, but say only a word and I will be saved.")
Everyone then goes up to receive communion; just because you are in a church, don't expect Italians to form neat, orderly lines! Once again, if you're not Roman Catholic, it's recommended that you stay in your pew. An American who has lived in Italy for several years explains that you won't be alone: "[The pews are] where most Italians will be, especially the men, since to receive Communion is to admit publicly that you haven't got any since your last confession. Humiliating, mortifying. Much better to arrive at church as the procession is starting and demand that the priest hear your confession then and there, so all your friends can pretend to assume you're coming straight from someone's bed. Much more satisfying."
Concluding Rites (Finishing Up)
The last prayers are mostly review from before: After the priest says "Preghiamo" finishes his prayer, everyone responds with what? Right, "Amen". After "Il Signore sia con voi", everyone says what? Right, "E con il tuo spirito." After the sign of the cross, another "Amen." Finally, the priest says "La Messa è finita: andate in pace" ("The Mass is ended: go in peace") and everyone responds "Rendiamo grazie a Dio"
There may be another song at the end.
The Traveller's Mass translates between a bunch of languages, including the Mass in English and Italian. This is a good guide to print out and bring with you so you can follow along. Once you get the hang of it, you can use Wikinapoli's Italian Mass One-Page Cheat Sheet (PDF link), reproduced below
Wikipedia's Mass (liturgy) page has lots of detail about the symbolism and history of the Catholic Mass.
Changes in 2020-2021: In late 2020, Italian bishops released a new (third) edition of the Italian Roman Missal (Roman Missal), which changed various parts of the Italian Catholic Mass, including a few major prayers:
Throughout (especially Penitential Rite): fratelli ("brothers") → fratelli e sorelle ("brothers and sisters") to be more inclusive
Glory to God: uomini di buona volontà ("men of good will") → uomini amati dal Signore ("men loved by the Lord") to be closer to the original Greek
Our Father: non ci indurre in tentazione ("do not lead us into temptation") → non abbandonarci alla tentazione ("do not abandon us to temptation") to make it clear that Satan, not God, leads to temptation