Check out the plugins documentation. You would need an event module that hooks into the events "a_post" for when an answer is posted, and "a_select" when an answer is selected.
If you need more pointers, check out some similar plugins from the Add-ons section, should give you some hints.
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.