Modal verbs (Can,Could and May) - English Learning Lesson

The lesson today is about Modal verbs -Can, Could and May-. These sentences uses if you're asking someone to help you. Yup ... there it is ... I hope i wouldn't make mistakes. hehehe ...

Modal verbs -Can, Could and May- has the sama meaning if you ask somebody to help you. But the level is May (More Polite than two others), Could and Can.
For an example :
May
- May i smoke here ? (At the restourant) - you don't know who they are
- May i borrow your dictionary ? (At the library) - yup, same like at the restourant

Could and Can
- Could you help me ? - you're asking your friend to help you - your friend
- Can you give me some water, please ? - your friend too

May uses for stranger people, you want to be polite, don't you? so use May if you want to be polite for asking someone help. But use can if they are your friend.

Sometimes i am confused about Could and Can, but today i don't want to figure out more further. Next time maybe i could give an example.