You can drag the dice to move them on the cards, a few people tried to click the die then click the card but that won't work.
Otherwise, does to die correspond to the attack's requirement? Under each card, you have what type of die they accept : a 4+ means 4 or more, even are evens, blank die is any die. And if the card has multiple dice under her, it will need more than one piled onto it.
Lastly, after you've used the card, it'll become grayed out and be unusable. Most of the time, it'll happen after the first use but some cards can be used multiple times, like Wink. The number of uses is shown in the red bubble on the top left.
If you still have a problem, it might be a bug ^^".
Could you describe more in details what you are doing? So I could check what's the problem?