I've been curious about this for quite a long time,I guess it's time to ask and know what it is xD.
So,at the cash shop section in the official site,I see that I have 5 "coupons",just like in these captures:


this one's the same but translated:



Can anyone explain what these "coupons" are for,and how to use them and all that?

You can use coupons for discount.

Alright then,thank you for the info :)