How does a non-refundable tax credit work?

How does a non-refundable tax credit work? I know it's a dollar for dollar reduction and once your liability is reduced to zero, you won't get any excess as an additional refund.

Example: If you typically get a refund each year, does this mean automatically that a non-refundable tax credit of $1000 is no value to you since you "don't" have any tax liability to pay at the end of the year?

Or am I misunderstanding and what would happen is you would actually get an additional $1000 back since you "overpaid" your tax liability by $1000 with the credit that's awarded.

Basic question I know.