How to navigate moments, collections, and years views in Photos for iPhone or iPad
Photos for OS X uses the same hierarchy as Photos for iOS — intelligently grouping images and videos into moments, collections, and years.
That lets Photos for OS X show you small moments in time and space, like yesterday at the park, but also collections of moments marked by larger changes, like that party across town or that week at the beach, and even an entire year all at once. That way you can quickly zoom out, drill down, or scrub through to find exactly the photos and videos you want to look at, edit, or share. And all it takes is a few clicks and swipes!
Full story from the iMore Blog...