When should the pronouns "tu" or "vous be used?

The pronoun "tu" is used in informal contexts. Situations where it should be used include:

• when you are speaking to someone in an age group close to yours

• when you are speaking to someone you know well (friends, family)

The pronoun "vous" is more formal. It is used when:

• you are speaking to someone who is significantly older than you

• you are speaking ot someone who is "superior" to you hierarchically (a colleague/boss, teacher)

• someone you don't know at all or just met 

When in doubt, use "vous" until the person you are addressing allows you to use "tu".