Retrieving photos from iCloud
How does one retrieve the photos that have been backups to the Cloud?
iPad Air, iOS 12
Question marked as
Top-ranking reply
Quick answer is this Download iCloud photos and videos - Apple Support
But, with your permission, I'd like to make you look further so you can be able to do a good management. So...
iCloud has two main functions, synchronization and storage, being the first one the central idea of it all when talking Apple's ecosystem.
If your pictures were taken with an Apple device logged with your Apple ID and the iCloud Photo feature is on, your photos are atomically synched with iCloud. See the article Set up and use iCloud Photos - Apple Support and the links in it.
If Optimize on iPhone/Optimize on this computer is on, the originals will be stored in the iCloud and you'll be able to access them on your devices, but the original larger files will be downloaded when you click/tap to open them.
That said, one way is you can then choose not to Optimize, so the orinals will be downloaded to your diverse, but you'll need storage space for it. See this Manage your photo and video storage - Apple Support and this How to free up storage space on your Mac - Apple Support (here you get the opposite ides, which is to preserve/free up space, but it talks about optimizing storage including photos)
Another way is to access iCloud.com on your computer, Photos section, and simply download them to your drive.