Tu and vous both mean 'you', however tu is much more informal and familiar and vous is more formal and polite. You would say tu when speaking to a friend, family member etc, and vous when speaking to an adult you don't know, a teacher or in a formal situation.

tutoyer means to call someone tu

vouvoyer means to call someone vous

It is often asked when first meeting someone: On peut se tutoyer? (Can we call eachother tu ?)