You can search for, browse, review, purchase, and download applications from the App Store directly to iPhone. Applications you download and install from the App Store on iPhone are backed up to your iTunes library the next time you sync iPhone with your computer. You can also install applications you’ve purchased or downloaded through iTunes on your computer when you sync with iPhone.
NOTE: The App Store is not available in all regions.
To use the App Store, iPhone must be connected to the Internet. See How iPhone Connects to the Internet. You also need an iTunes Store account (not available in some countries) to download applications. By default, iPhone gets your iTunes Store account settings from iTunes. If you don’t have an iTunes Store account, or if you want to make purchases from another iTunes Store account, go to Settings > Store. See Store.