When do I know whether to use "tu" or "vous"?

In French as well as Spanish and a few other languages, we have 2 different ways of addressing people: using the "tu" or the "vous".When talking to a friend, someone we know quite well or someone who is around the same age as yourself that you feel comfortable talking to, we use the "tu". Ex: "Tu en penses quoi du nouveau film de Disney?" (What do you think of the latest Disney movie)However when talking to an authoritative figure such as your boss, your teacher, professor at university or just someone you've never met or talked to before, it is necessary to use the "vous": "Est ce que vous voulez du lait avec votre cafe?" (Would you like some milk with your coffee?)The 2 different manners to address someone exist as to not offend someone you don't know by coming across as overly friendly and to maintain a certain distance when talking to strangers or someone you respect. Therefore it is important to pay specific attention to the person you are talking to and how well you know them as to not use the wrong person. However, it is possible to first use "vous" but then using the "tu" as you become closer to the person when appropriate.