Let's start from the basic greetings and idiomatic expressions:
“Good morning” is translated with buon giorno: this is the formal expression Italians use with people they jut met or with elderly people in sign of respect.
A more familiar expression to say “good morning” is ciao: this can be used both to say “hi” when we meet someone, or when we are leaving.
“Good evening” is translated with buona sera; again, you can replace this expression with ciao when you know the people you are talking to.
To say “thank you” to someone, you say grazie or molte grazie to put emphasis on the sentence (it means that you are really grateful).
When you are leaving a place, such as a shop or a restaurant you can use the expression arrivederci, that is the correct translation for “goodbye”, or a presto, that means “See you soon”, or “see you later”. (Italian people do not really mean they are going to come back later).
When you ask a question remember to say per favore, that means “please”
Now that you've learned the basic greetings you can start with some useful Italian words:
Food and drinks:
“Water” is translated with the word acqua: you may need to buy or order una bottiglia di acqua, that is "a bottle of water".
Wine: you may want to enjoy some good Italian wine. If you rather “white wines”, ask for some vino bianco, while if you rather the “red wine” you'll say vino rosso. According to your preferences, you can order just “a glass of white” or “a glass of red wine”. Then, ask respectively for un bicchiere di vino bianco, or un bicchiere di vino rosso.
Don't forget to try some Italian freshly-baked bread, so ask your waitress for un po' di pane, per favore that means “some bread, please”.
You may not need translation for prosciutto or mozzarella.
Remember that we don't have “ice cream” in Italy, but the gelato.
If you decide to go around by using the public transports you should know that “the underground” is la metro (no accent on the last vocals). If you want to ask someone for directions, such as “where is the underground station?”, you say dov'è la metro?
The word for “bus” is pretty similar: autobus.
Same thing for the “cab”, in Italian we simply say taxi.
Now that you've learned these key Italian phrases and words you'r ready to travel to Italy and to interact with local people.
Have an amazing journey to Italy