I can cook a delicious meal for dinner tonight.
I can speak three languages fluently.
I can run a marathon in under four hours.
I can play the piano and guitar.
I can solve complex math problems quickly.

I cannot dance very well.
I cannot understand this complicated physics problem.
I cannot eat spicy food because it upsets my stomach.
I cannot stay up late at night, I need my sleep.
I cannot swim very well, so I always stay near the shore.

Can I borrow your car for the weekend?
Can I have a glass of water, please?
Can I ask you a question?
Can I use your phone to make a quick call?
Can I have a day off work next week?