It's a common and versatile question that can be used in many situations, like:
* To ask someone about their current activity: "Que faites-vous en ce moment?" (What are you doing right now?)
* To politely inquire about someone's work or occupation: "Que faites-vous dans la vie?" (What do you do for a living?)
* To ask about someone's plans: "Que faites-vous ce week-end?" (What are you doing this weekend?)
The phrase is also used to express surprise or disbelief, similar to "What are you doing?!" in English.