Here's how you can use it:
* Informal: "Qué pasa, amigo?" (What's up, friend?)
* Formal: "Qué pasa, señor?" (What's up, sir?)
It is important to note that while "qué pasa" is a common way to say "what's up", it is not the only way. You can also say:
* ¿Qué tal? (How are you?)
* ¿Cómo estás? (How are you?)
* ¿Todo bien? (Everything alright?)