"What can I say" is something you say when you don't have any other good response to what someone says. Some situations where you can give this answer include:
- When someone says something really good about you, and you agree but you don't want to brag.
- When someone is really angry about something, but you aren't able to fix their problem.
- When someone criticizes you, and you agree that it's true.
You can use it like this:
A: You're such a good singer!
B: Yeah, well, what can I say? It's a gift.