As I understand it, it's automatically generating it's own keywords based on what seems to be common on the page, then selects something appropriate for the discussion and your location. You should see ads that are relevant to you, and in some cases you may be the only one that see's them.
If you (or anyone else) see any ads that don't seem right, please let me know what the ad is (who it's for and the domain if possible) and I'll see about having it removed.
Def