Install iTunes on your main computer before trying to use your iPhone/iPad/iTouch.
Currently, Priacta recommends either IMExchange 2 (for Exchange Server, find it in the App Store) or Pocket Informant for iPhone/iPad/iTouch (for desktop sync, see www.pocketinformant.com). Neither of these is perfect: IMExchange 2 is a good app but has marginal tech support, and Pocket Informant only supports desktop WiFi sync (an Exchange sync is being considered). Choose the one that works best for you, and test it before relying on it.
IMExchange 2 sync setup instructions can be found here: https://rerlsoft.com/home/FAQ_And_Contact_Details.html.
Pocket Informant for iPhone/iPad with WebIS Desktop Sync
Other Sync Options
If you rely on some other app, go to the publisher’s web site for syncing instructions. Be sure to leave a comment below sharing your experience, so everyone benefits.