For example, click on your “profile” and check out what ads are showing.
If you see something you don’t like, simply hold your mouse over the upper right hand corner and click the “x”. This is equivalent to you reporting the ad to Facebook and saying “hey, I don’t want to see this ad…”
Likewise, there is now a “Like / thumbs up” button you can click to give an ad a vote of confidence as well.
Facebook appreciates this feedback since their ad system has a reputation of being extremely targeted.