Family Sharing is one of the most promising feature of iOS 8′. It's a feature that's close to Apple's integration philosophy. With Family Sharing, you can share content that you buy with other iDevice users in your family.
If you bought an app or a song, with Family Sharing, you can share that app or song with other members of your family (those who use an iDevice running iOS 8). This means you don't have to buy multiple times, or use complicated steps to sync the content across all devices.
How to Setup Family Sharing in iOS 8 on iPhone/iPad:
Step 1: Go to Settings → scroll down and tap on iCloud
Step 2: If you're setting up Family Sharing for the first time, tap on Set Up Family Sharing.
Step 3: Tap on the Get Started at the next screen
Step 4: Now tap on Continue, if you want to continue with the logged in iTunes account, or tap on the want to use a different ID at the bottom of the screen to change your iTunes account.
Step 5: At the next screen, tap on Continue to confirm Share purchases. Again press continue at the next screen to confirm your payment details.
Step 6: At the next screen, select Share Your Location, if you would like to share your location with your family members or choose Not Now
Step 7: After this, tap on Add Family Member.
Step 8: Enter the Apple ID of the person you want to add to the Family Sharing and then tap on Next. Invitation to join the sharing will be sent to this Apple ID.
You can repeat the process to add more family members to the Family Sharing.
Here's something you should note though: every member in the Family Sharing club needs to have the same credit card data as the main account holder. But worry not because every purchase “request” is sent to you for your approval. So if your kid decides to purchase a game, you will get a notification (lockscreen, alert) requesting your permission. If you decline, that purchase is not made.
There's another catch: Family Sharing is not a global feature available with every app, music, movie or any other content by default. In fact, it looks like developers and content creators need to enable Family Sharing comparability in order for you to share it with your family members.