In French, there are two words for "you".
"Tu" is the singular you. But you use it when addressing to someone you know well (friends, family) or a child.
"Vous" is the polite/formal "you" or the plural "you". So, you can use "vous" when addressing to one person or to several persons.
When adults meet for the time, "vous" is used. You have to continue to use "vous" unless one of the adult says "On peut se tutoyer." (We can use "tu" with each other.) or "Vous pouvez me tutoyer." (You can use "tu" with me).
So, it's important to know when to use them as you could be rude if you pick the wrong one. When in doubt, it's always best to "vouvoyer" (use "vous") someone.
