You just did. Just make a new post and it becomes a question. The prefix is automatically assigned. Then responses become answers that others can vote on. If an answer post receives a score of 5, that post is automatically marked as best answer, but you can also choose the best answer yourself among the responses. Once best answer is marked, the thread gets Answered prefix automatically. If another answer gets a score higher than 5 and is higher than the current best answer, it gets automatically set as the best answer.