When you first get your iPad or iPhone, it comes with several applications already on it. But that is not all you can use it for. The app store has thousands and thousands of apps that you can add to your device. There are two main ways to add apps, the iTunes store and the App Store on your device.
Once you have purchased apps from your iTunes Store, may automatically download to your iPad, iPhone, or iPod. But for some reason you have deleted your app you can always download it again.
You can change the settings on the iPad so that if you buy a song or app on your desktop machine (or other iOS device) it will automatically download to your iPad.
You don’t have to use iTunes on your desktop machine, but if you do, you can log in to buy apps, songs, movies, and so on. If you use a desktop macine, you can backup your iPad to it, and so on. I use my desktop machine to store all my iTunes songs movies, and TV shows. The reason is that I have got too many to put on my iPad at one time so I need somewhere to store them.