Summarize this article in one sentence.
On any device, find the iTunes application. You may also find out your balance by opening iBooks or the App Store and following the same steps. On computers, look along the top of the screen. You’ll see the word “Store.” For example, when you are looking at your music library, the headings under the playback bar and navigation bar at the top of the screen will start with “Library” and end with “Store.” Click the "Store" button.  The "Store" button can be found the same way in any part of your library. No matter if you’re looking at your music, videos, podcasts, or other media, it will be in the same location. Another way to quickly get to your account balance is to click the “Account” button on the navigation bar at the top of the screen. Click “View My Account” on the drop-down menu. On iPhone, iPad, and iPod devices, scroll to the bottom of the screen. On a computer, the account balance will be in the upper-right corner of the screen. On a mobile device, if you don't see your user ID, tap the "Featured" button at the bottom of the screen, then scroll down. If you are not already signed in, tap the sign in tab at the bottom of the screen. On a computer, click the “Account” button at the top of the screen, then click “Sign In” on the drop down menu. Enter your Apple ID and password or create an account. Once you sign in, the sign in tab on mobile will display your Apple ID. Under it, you’ll see a number such as “$25.00 credit.” On a computer, this will be in the upper-right corner of the store. If you know how much money is supposed to be in your account, you may be able to figure out whether or not you’ve redeemed the gift card.

Summary:
Open the iTunes application. Navigate to the iTunes store. Locate your account balance. Sign into your account. Look at the account balance.