The majority of your mobile app testing can be performed on your PC using Titanium's virtual device emulator window.
This tool offers a pretty good imitation of a real mobile device (iOS, Android, Blackberry, etc), including a complete graphical interface, complete with familiar features such as icons, menus and device unlocking.
However, it's not perfect.
Depending on the PC your using for development, you're probably missing out that all-important touch-interface experience.
And if your app interacts with the built-in camera, accelerometer, various other sensors or GPS positioning system can only be fully tested by using a real handset.
The steps necessary to deploy your app onto a real smartphone or tablet varies depending on the device brand and type.
For Android, with it's USB interface, it's a fairly straightforward procedure. But when it comes to Apple devices you'll discover connectivity restrictions make iOS app deployment a rather more complex process.