Difference between Can, May

The difference between
Can and May

Many English speakers are confused about the usage of the words ‘can’ and ‘may’. For e.g., ‘Can' I drink water?’ is incorrect. ‘May I drink water?’ is the correct phrase to use in this case.
The key difference between ‘can’ and ‘may’ is that ‘can’ talks about ability and ‘may’ talks about permission.

CAN
Can is used in two cases:
To talk about ability.
I can finish my homework by 5 pm.
Can you finish your homework tonight?
To ask or give permission informally.
Can I use your pen? (To a friend)
You can use my pen. (To a friend)

MAY
May is generally used to ask or give permission formally.
Let us take a situation between a student and a teacher.
May I drink water?
Teacher: Yes, you may.
Let us take a situation between two strangers.
May I borrow your pen?
Yes, you may.