It's a casual and friendly way to ask someone how they are doing, similar to saying "What's up?" or "How are you?" in English.
Here are some other ways to express the same sentiment in Spanish:
* ¿Cómo estás? (How are you?)
* ¿Qué tal? (How's it going?)
* ¿Todo bien? (Everything okay?)
* ¿Cómo te va? (How's it going?)
The choice of phrase depends on the context and the level of formality.