New Year Gifts Discount?

Among the New Year Gifts from Warmane this year (btw thanky ou Warmane!) I received a 30% discount code. How and where can I use it though? When donating for coins I get thrown straight to my credit card number, not given any chance to use any discount code anywhere?! :) I am slightly confused and will appreciate any answer to this puzzle.

Thank you!

You can use it when buying items from Store. In the confirmation popup there is a field where you can enter discount code.