How to refresh iAd and specify keyword manually?

I successfull开发者_如何学Goy integrated iAd into my iPhone app. However, I can't find a way to refresh the ad manually. I couldn't find a way to specify keywords for the ad either. How does iAd work after all? Does it just show some ads randomly?

iAd is totally controlled by Apple based on keywords, the app type and exclusions that you set when you release or modify the app on Itunes Connect. The ads are served only when you release it via ITunes Connect.