Please note that the group of people who match the audience’s selected characteristics will of course get smaller the more selections you make!
On the right side, you can see a needle (displaying the audience size) that shows if the size of your selected audience lies in the red or the green area indicating if it's size is too small, too big or appropriate. It is recommended to put an effort into setting up the audience as correctly as possible as this will facilitate all further actions.
Now you can choose where you want to place your advertisement. It can either be placed automatically or individually.