when I've chosen the best answer to my question, how and where do i let this site know who I've chosen?

After 4 hours has passed and up to 4 days, if few answers are forthcoming, a blue "vote" button will appear along with each answer. Choose which you think is best and click on that button.

You need to wait 4 hours before you can vote for best answer. a blue button will show under each answer. Choose your best answer and click the blue button under it. You then can rate with 1-5 stars and leave a comment. You will get 3 points for voting. You have up to four days to vote before it goes to a community vote.

If its an other members question that you want to vote on you need wait for 4 days or more then go back to the question and vote you will get 1 point for voting.

well go to the you have a new answer,when you are there it will say chose the best answer on each answer.you just click that spot and then it will give a place to comment on the answer you choose,so people will understand why you picked that particular answer.try it on this question,and if you succesfuly selict my answer as best then you know how to select them in the future,P/S always pick mine where you can

well, you have to wait until maybe a day passes since you've uploaded your question, then you will see a blue button under each question that says choose as best answer. whatever answer you choose, you have to click on the blue button underneath it

When you click the 'choose' button and 'submit', you've told the site and they'll take care of the rest.