"où" means where. Here are examples that will help you understand how to use "où". It is the same as in English:

There is a grave accent on "où" to tell the difference with "ou" (or) but the pronunciation remains the same.

• Où habitez-vous ?
  Where do you live?
• Où partez-vous en vacances ?
  Where do you go on holidays?
• D'où viennent-ils ?
  Where are they from?

• venir de quelque part
  to come from somewhere