Can, Could to ask permission or make questions

Can is used in a more informal way of asking questions.

Can I come in?

Can I sit here?

Can I get a sheet of paper?

Yes, you can come in.

Yes, you can sit here.

Could is used in an informal way to make questions.

Could you lend me your pen?

Could I have a glass of water please”

Could I know your name?

You could ask his permission.

You could sit keep your bag there.