iCloud: What is iCloud Photos?
iCloud Photos keeps your original photos and videos safely in iCloud. With the originals stored in iCloud, you can keep smaller versions on your devices to save space. iCloud also makes it easy to enjoy your photos anywhere, and from any device. If you add photos and videos on one device, they appear on all your devices.
You can access, store, and update your photos, Live Photos, and videos using iCloud Photos, Shared Albums, or My Photo Stream, and share them using a link in iCloud or Shared Albums.
iCloud Photos automatically stores every photo, Live Photo, and video you take and gives you access to your photo library on iCloud.com, your iOS devices, your Mac, your Apple TV, and your Windows computer.
You can create Shared Albums and invite friends and family to post their own photos, videos, and comments.
My Photo Stream
My Photo Stream uploads your photos from the last 30 days, up to 1,000 photos, so you can view them on all your devices in the My Photo Stream album.
Note: My Photo Stream is not available for newly created accounts. See Keep photos up to date across devices with iCloud.