In French, there are two forms of 'you' when talking to a single person: 1. 'Vous' which is the polite form, used in situations where showing respect is appropriate 2. 'tu' which is the more casual form, used with friends and familiar people

The confusing part is that 'vous' also means 'you' when talking to multiple people. Sometimes it can be tricky to decide which is meant - you have to judge by context and the form of the verb.

"vous" can be used to address one person when you want to be polite.

Just like xRyanx said, "vous" is typically used when talking to an adult

Yes if it is more then one person or if you meet someone for the first time you'd say vous instead of Tu. Also if you are talking with a teacher or an adult you'd use vous unless if the adult is related to you then you would use Tu.