iCloud Photo Sharing is part of Apple's iCloud service, and lets you share Photo Streams with your friends and family. You can find these shared streams in the Photos app, under Shared; the list contains any shared streams you've created as well as any you've been invited to. Once you've enabled shared Photo Streams on your iOS device, you'll instantly have access to iCloud Photo Sharing in the Photos app.
How to view shared Photo Streams on iPhone and iPad
Launch the Photos app on your iPhone or iPad.
Tap on the Shared tab in the bottom navigation.
Tap on Sharing at the top to get to the main view.
If you don't see a shared tab, you'll need to enable shared Photo Streams first:
When you open the Shared tab in the Photos app, by default you'll be viewing the Activity stream. This section is an overview of all your shared streams and shows you what's been added recently, along with any comments or likes on images you or others have taken. If you tap on the Sharing button in the top left corner, you'll be taken to the full list of all of your shared Photo Streams.