Look to the top right corner of any answer to your question. There will be a faded green checkmark. Click on it, and you'll select that answer as the 'best answer' (BA). You don't need points to select the BA.
If you receive an answer that totally resolves your question, then please select the answer. If no answer is selected for a particular question after some time passes, and the moderators believe there is an answer that should be selected, then they may select it on the asker's behalf.
You can only see the green checkmark if you are the original author of the question, or if you are a moderator. Selecting the best answer is not a permanent action — you can de-select an answer or select a different one at any time.
Selecting the BA awards you two points, and having your answer selected awards you 20 points. You can read more about the points system here.
