In French, there is 2 ways of saying "you". It can either be "tu" or "vous".
If you are speaking to an adult you don't know, your boss, your teacher or any adult that is not friend or family, you will be expected to call him "vous" unless he tells you otherwise. When you address someone as vous : you need to use the following pronouns : vous, vos, votre...
If you are speaking to a child, a fellow student, or a friend/family member you will call him "tu". You will use the following pronouns : tu, toi, tes, ta, ton...