Prior to iOS 7 you could share a Photo Stream with friends and family but they could only comment on photos and view them. It left a lot of people not wanting to use Photo Stream due to the lack of full functionality and usefulness. Luckily, iOS 7 has changed that and now allows you to let other people contribute photos too.
That's all there is to it. Anyone you invite to that Photo Stream now has the ability to add photos to it. This is great for family members especially when on vacation or for photos of children. Just keep in mind that all users will need to be running iOS 7 or later to add photos to someone else's shared Photo Stream.
Let us know what you think of Photo Stream now that you can actually collaborate on photos more efficiently with iOS 7.