(Note that can is less formal than may. Also, some writers will object to the
use of can in this context.)
Request (Requests usually refer to the near future.)
Can you give me a lift to school?
Can you pick me up?
Could you tell me the time, please?
Possibility or Probability
You can't be 45! I thought you were about 18 years old.
Learning a language can be a real challenge.
Anyone can become rich if he tries to save money.
For examples:
I can play a piano. - positive
I can’t speak French. – negative
Can/Could you open the door, please? – question
Can/Could I have these postcards, please?