The Best Answer feature allows you to highlight the reply that best answers your question, reward the helpful member who posted the response, and a great way for others find the answer to the post quicker without having to read through an entire topic.
Any topic you've marked as best answer will be solved and appears in search results with a checkmark. Future visitors searching for an answer to the same question will be able to click through to the answer quickly.
Marking Best Answer
When you receive a response to your post that answers your question, click " ✔Best Answer" on the bottom of the answer. The post will be marked by a SOLVED green tag. The best answer is also shown in the beginning of the thread below the original question for future visitors to quickly find the answer.

Unmarking a Best Answer
If you change your mind, or if another reply provides better answer, you can unmark your first selection and accept the second reply as an answer instead. To unmark a Best Answer, click “× Unmark answer” at the bottom of the answer. You can then choose another answer.

Now that you're familiar with the functionality, get out there and start showing your appreciation to your fellow members by marking their replies as "Best Answers"!