Syncing with iCloud
To access iCloud Photo Sharing on your Mac, you'll use either iPhoto or Aperture. You'll need to go into one of these programs (for most people this will be iPhoto) to enable iCloud Photo Sharing.
If you don't see the iCloud Photo Sharing option, your software may not be up-to-date. You can purchase the most recent version of iPhoto or Aperture in the Mac App Store.