Just run software update on your Mac, and you'll see it. 

The next big release of OS X, named “El Capitan”, is here. Go forth and download!

Mac OS X El Capitan Photos features

Here's what the official release has to say about Photos…

New ways to organize and enhance your images in Photos.

• Photos automatically organizes your library and helps you edit like a pro with simple and powerful editing tools.
• Access your library on all your devices with iCloud Photo Library.
• Add or edit location data, and batch change titles, descriptions, and keywords.
• Sort your albums and the photos in them by date, title, and more.
• Use third-party editing extensions to take your photo editing to the next level. 

And that last one there is, of course, the big deal. Finally we get Extensions support in Photos for OS X!

As you may have already seen, MacPhun was the first to release apps with Photos Extensions support. Check it out!