From the home screen, tap the App Store.
From the App Store home screen:
Tap the preferred sort option.
Tap the purchase price or GET.
For free apps, tap INSTALL.
Tap the preferred option.
Note: If prompted to Sign in to iTunes Store, enter the Apple ID details and tap OK.
If prompted to verify payment info, tap Continue. On the Account Settings screen, tap the preferred Payment Type and enter the Card Details and Expiration Date. Verify the Billing Address and Phone number are correct. When finished, tap Done.
When finished, tap OPEN to launch the application or press the Home key to return to the home screen.
The preferred application is installed and ready for use.