Greetings

Buongiorno (lit: good day) - hello, good morning, goodbye

Buonasera (lit: good evening) - used for late afternoon and evening

Buonanotte - goodnight

Arrivederci - goodbye (at any time of the day)

NB. Italians normally use titles when addressing each other formally:

Buongiorno, signore (Good morning, sir)

Buongiorno, signora (Good morning, madam)

Buonasera, signorina (Good evening miss)

Grazie, dottore. Arrivederci! (Thank you, Doctor. Goodbye)