"S'il te plaît"
Politeness. Usually if you're talking to someone you don't know, or someone that deserves respect (ie and elder, a supervisor, your girlfriend's parents...) you would use "vous". If you're just talking to a buddy, you would use "te". Ditto for other situations. If you know the person use "tu" for you. If you don't know them or they're your boss, use "vous" for you. That's my take on it, but I'm not a native speaker.