Every answer generates a donation. But I don't see the pink star under your profile pic. Perhaps you should try again to sign up for it. Just hover your mouse pointer over the star under someone else's pic and click on the "What's This" link and proceed from there. Good luck and thanks for supporting the cure.
Only the answers you give that fall within the community guidelines contribute .25 for each answer. In other words, just try your best to give helpful answers (% oh, and try to avoid answering questions that violate the guidelines also, the question and the donations will be removed on those.