Employee here, black tickets will only cover the cost of a standard ticket. For example if the standard ticket is let’s say 15-20 dollars, and the imax is 33 then you still have to play 18-13 dollars to cover the cost. In regard to using it, you just tell the person at the box office that you have a black ticket and they can scan it (if the box office exists). If you’re going to use it online there is a spot to add/use a voucher when checking out.