What's the difference between "du" and "Sie"?
Du - you
Sie - you
"Sie" is more formal. Germans usually take it seriously, so if you are talking to someone you don't know, asking for information, prefer to use "Sie". Also at school, talking to teachers it is always used.
*Notice that "Sie" is used for:
-"Sie" - you - both singular and plural (formal)
(always with the -S- capital
- "sie" - for she
- "sie" - for they
Don't worry, you will always know which one is which. You use different conjugations with each one and also by the context :)