It's kind of a puzzle to me, so I look forward to other replies. But from what I can see it's not an app that you can download and install, but more of an online service. I back up my Apple devices to the cloud. That works pretty well. But I too have found that the only way to access things there directly is by going to icloud.com. And even the things that are there are hinky. You can't delete photos - or you can but only in a certain way. If you take a video with your iPhone, it won't get shared via Photostream to your Mac through the cloud. You have to plug the phone into the mac and then use something like Preview or iPhoto to download the video from PhotoStream. Ridiculous!