How are accepted answers approved?

Only the thread author (the person who created the thread) can accept an answer.  So only one reply per thread can be the accepted answer at a time.

1. The thread author sees an "Accept" button on each reply
2. Clicking it sets accepted on that reply.
3. If a different reply was previously accepted, it gets unaccepted first so only one reply per thread can be the accepted answer at a time