Over the past few years it has been possible, but never easy, to have a family with iOS devices where everyone could share purchases but keep their own accounts for other purposes. Thankfully, Apple has recognised this pain point and introduced Family Sharing in iOS 8 which not only streamlines the ability to do certain things that were possible before, but also introduces some new features that makes having a family with iOS devices easier to manage.
To summarise the changes, everyone in a family can now have their own Apple ID but if they also enroll in Family Sharing they will be able to share App/iTunes Store purchases, Photos, location (Find My Friends/Find My iPhone), Reminders, and Calendar events between everyone. Most of that was possible pre-iOS 8 with some trickery and effort, but Family Sharing simplifies it significantly. What is new with Family Sharing is the ability for everyone to have their own Apple ID and share existing purchases or request purchases which will be made from one central account.