Let's see.... Salve is an introductory phrase, ideal when you enter a shop full of customers and you pass by the clerk...You say "Salve" and go inn. Also when you find a group of person and in that group there's someone that you know, you say a collective " Salve!" along with a nice smile, and everything is going to be OK. Buongiorno is not formal, it's normal when you're supposed to get and answer or a service from someone. I'll give you thre examples fo the different uses of Salve, buongiorno (o bunoa sera) and "ciao". 1st: You're in Milano and you see a nive pair of shoes in a shop. Yuo decide di go in justo to have a glimpse, and you say "Salve" when you pass by the clerk, IF HE OR SHE IS BUSSY. Is she or he is alone , the prhase should be "buongionro" o "buonasera". 2nd: You get itno a cafeteria to have a capuccino: You should say "buongiorno", but salve is not totally impolite. In te North from Italy, it's quite normal. 3er: You're strolling down the street and you see someone you know: you must say "ciao" if he or she is of you age. If he or she is an older person, say Buongiorno. When you leave, you always say "arrivederci" (to see us again) and "ciao" if you're friends. There's a very formal way to say good by when you don't have a friendship relation with your interlocutor and it's :Arrivederla, which means " to se YOU again", but that "la" at the end is the "respect" pronoun. In Italian ( as well as in Spanish or German) you have two different pronouns for "you"; one for the friends, the people you're familiar with, and another one for people you don't know of people who deserve a respectful treatment. In Spanish tu and usted. In German du and Sie, in Italian tu and Lei. Ciao...Arrivederci