Asking Permission

Modals are commonly used for asking permission

Can I ask you a question?

May I have a piece of cake?

Could I get you to turn off the lights

Some other common phrases are

Do you mind if I smoke?

Would you mind if I asked you something?

Is it okay if I sit here?

Would it be all right if I borrowed your lawn mower?

Giving Permission

Sure.

Go ahead.

No problem.