Since all iPad apps come from the same source (namely the App Store, or iTunes Store), Apple keeps track of all versions and sub-versions of apps as they are released in the store by their developers. And since, whenever you install an application on your iPad from the store, its version number is listed, it is very easy to figure out if you have available updates for one or more of the apps you have installed on your device, as you'll learn in this tutorial.
Here are the simple steps to follow to check for updates for your iPad apps:
This is all it takes to check for new updates for your iPad apps; note that this approach allows you to update your iPad from the device itself. But Apple also lets you do the same thing from iTunes: once you plug your iPad into your Mac or PC, iTunes will automatically check in the App Store for new updates, and tell you about them. It doesn't matter how you install your app updates, your iPad and iTunes won't install them twice.