This is a picture which explain if you have to say "tu" or "vous" http://3.bp.blogspot.com/-ZguDl4NL1t8/U8WheWDTAPI/AAAAAAAAHFE/XnW_CdPdxEc/s1600/tutoyer-LA-times-tu-vous-french.jpg

"Vous" is formal/polite, you'd use it when addressing to someone older (typically if you're a child/teenager speaking to an adult), to a teacher/boss, or to someone you don't know (if you're both "old"; two teenagers would use the "tu" between them for instance even if they don't know each other). The "tu" is typically used with family and friends. In case of doubt use "vous" so that you're sure not to make an impair! I hope this help! ;)

The same as in person.