If you have created a Q&A you can select a Best Answer. This will allow other users of the Q&A to save time when viewing the Q&A as well as letting the responder know that you appreciate their efforts.
To do this, place your cursor over the response and three dots will appear. Select the 'Flag as best answer' option and their response will be highlighted.
To undo this, click on the cog again and select Remove best answer flag or simply award the best answer to another post.
Note: Only the creator of a Q&A can award the best answer.