It's used to express acceptance of something that is unfortunate or unavoidable. It's a way of saying, "What can you do?" or "Life happens."
Here are some examples of how "sa la vie" might be used:
* "I lost my job, but sa la vie, I'll find another one."
* "The weather's awful today, but sa la vie, what can you do?"
* "My car broke down, sa la vie, I'll get it fixed."