What is the difference between "tu" and "vous" and when should you use them?

In French, the personal pronoun "you" is translated in two ways: "tu" and "vous". "Tu" is the second person singular, and "vous" is the second person plural. "Tu" is singular, which means that you use it when you address one person: ie. "Tu es gentil" ("You are nice"- only one person is nice here). Whereas "you" is used when you address more than one person: ie. "Est ce que vous êtes prêts?" ("Are you ready?"- a large group of people). However, sometimes you have to use "vous" for just one person. This exception is used when you have to address an adult if you are a child, or someone that you have to show respect to. For example, if I speak to a teacher, unless told otherwise, I need to say "vous": ie. "Vous m'aidez beaucoup" ("You are really helping me"- to my teacher, just one person). My teacher also needs to use "vous" when talking to the director, or a parent, as they have to show them respect.