In Italian it is very important, in order not to make mistakes talking to somebody, to learn as soon as possible the difference between two diffent verbal sujects: “Tu” and “Lei”.
“Tu” is used when you talk with a friend, a child, a family member or someone you know well.
Es: Paolo, tu come stai? Luigi dove vai?
“Lei” is very formal and used when you talk to someone you don’t know, or with whom you don’t have a friendship, such as, for example, in a business meeting, with a teacher at school, with a doctor in the hospital, when you go shopping, when you ask for information. Es: talking to the doctor: “dottore, come sta”? Talking to the teacher at the school: Professore, dove va?
Be careful: we also use “Lei” for the feminine third person, but the meaning is different.
Es: talking about Maria, you can say: Lei (Maria) oggi va a Roma e torna domani.