In modern, standard English, there is only one form. Whether you’re talking to one person or a group of people, to a VIP or a child, the word is “you”. In French, it is different: there are two words for “you”, tu or vous.
Here is an explanation of when to use each:
When you are talking to more than one person, use vous = collective you.
e.g. What are you (all) eating? Qu’est-ce que vous mangez?
When you are talking to a person you do not know very well and you want to be respectful, again use vous = polite or formal you.
e.g. Can you help me? Pouvez-vous m’aider?
When you are talking to someone your age or younger, with whom you feel comfortable and whom you now feel you know a bit better, you can use tu = friendly or informal you.
e.g. What’s your name? Comment tu t’appelles?
e.g. Do you want to go for a drink? Veux-tu prendre un verre?
With practise, you will know instinctively whether to use tu or vous. In the beginning, it is safer to start off using the polite form vous so as not to risk offending anyone, but French people will understand that you are not being intentionally rude if you use the wrong form. Usually, they will put you at your ease by saying to you on se tutoie or on peut se tutoyer which means we can call each other “tu”.