iCloud Photo Library allows you to access all your pictures and videos from anywhere through the web.
Sure, the Photos apps for iOS and OS X are fast, convenient, and loaded with features, but there might come a time when neither of them is available to you. That's when iCloud Photo Library being part of iCloud really comes in handy — because you can access everything you have online straight from any web browser you have. All you need is a stable internet connection, your Apple ID login details, and iCloud.com.
It should be noted that it might take a while the first time you load iCloud Photo Library on the web. If you see Preparing Library..., either be patient or come back later. Even if you leave iCloud.com temporarily, your library will still continue to populate. So don't worry. This should only happen at the first time. Once it's done, your entire photo library will appear and subsequent loading periods will be much, much shorter.
How to access and view photos in iCloud Photo Library on the web
1. Launch any web browser and then go to iCloud.com.