"CAN" AND "MAY"

"May" asks permission:

May I see your driver's license?   =   I am asking permission to see your driver's license.

May I see some personal identification?   =   I am asking permission to see your personal identification.

"Can" asks if someone is able:

Can you tell me where the store is?   =   I am asking if you are able to tell me where the store is.

Can you tell me where to find groceries?   =   I am asking if you are able to tell me where to find groceries.

Example:

Do you have a phone? May I call you? Can I reach you by phone?