Pressing the ‘Start Sharing’ button opens up the Preferences panel for Photos, and then takes you into the iCloud section.
Photos provides three different options for sharing your photos – iCloud Photo Library, My Photo Stream and iCloud Photo Sharing.
These options are also available in the Photos app for iOS 8, so most of the steps we show you here will work in a similar fashion on your iOS devices too. We’ve seen My Photo Stream and iCloud Photo Sharing before, as they were originally available in iPhoto too.
Let’s turn on just those two options for now, and then we’ll come back to the new iCloud Photo Library later.
How to use the Photos app in Mac OS X, set up and use Photos for OS X and
Photos for Mac review