May or Can?

[Depaula]

I'm confused. When I use MAY or CAN in the question:

May I help you?
Can I help you?

What is correct?

Thank you!!!!

[Tetsuo]

Hope that I'm not that wrong but my teacher told me that using "May" is more polite and that you can use both of them.

[need to learn]

Depaula,

Tetsuo is correct.........Jackie