Airprint to an HP c7180

http://www.apple.com/ipad/features/airprint.html

when your printer is not on the list

you have to download a special hp app from app store

and or look for other 3th party apps which handle printing

Yours is not an 'Airprint' enabled printer (there is a list kindly posted by Rudegar), your printer is not on it so as previously recommended you'll need an app, try print n share, printcentral or others.