There's nothing to explain actually, just look at the screenshots and you'll get it:
The popup window prabably needs to be smaller though.
If you refuse donation or don't click anything for 10 sec, the donation is redirected to the next available player.
Another thing I wanted to sort of remind Aza is this:
I posted it in skype and he said it's possible but never mentioned if he is going to implement it or not.Speaking of ks, I wanted to ask about one thing. Is it possible to change a donation system that once you donated ks2 it will reset your streak and you can earn another one without dying? Might be a reason for skilled players to use it - you can stay alive and still benefit your team.
Or maybe make the donation reduce the amount of kills needed to claim the next streak. Would provide a slight advantage but not a game-breaking one, since you should still stay alive really long to use it