Use iCloud Photos to store photos in iCloud
With iCloud Photos, all the photos and videos in your photo library are stored in iCloud, so you can access them from your Mac, PC, iPhone, iPad, or Apple TV, and on iCloud.com.
Any new photos and videos you add to Photos, or take with an iPhone or iPad, appear on all your devices that have iCloud Photos turned on. Your photos and albums are organized the same way on every device, and if you make edits or remove items, you see the changes on all your devices.
Before you set up iCloud Photos, update to the latest version of macOS, or the latest version of iOS or iPadOS on your device. See the Apple Support article Set up and use iCloud Photos. For information about using iCloud Photos on a Windows PC, see the Apple Support article Set up and use iCloud Photos on your Windows PC.
Turn on iCloud Photos
If you’re not already signed in with your Apple ID, choose Apple menu 
In the Photos app
on your Mac, choose Photos > Preferences, then click iCloud.Select the iCloud Photos checkbox.
Select one of the following options:
Download Originals to this Mac: Stores the full-size versions of your photos both on your Mac and in iCloud.
Optimize Mac Storage: Stores smaller versions of your photos on your Mac when storage space is limited, and keeps the original, full-size photos in iCloud. Choose this option to conserve space on your Mac. To restore the originals to your Mac, just select “Download Originals to this Mac.”
When you first turn on iCloud Photos, it can take a while to upload your photos to iCloud. You can continue to use Photos while your photos are being uploaded.
Tip: To temporarily pause uploading or downloading of photos and videos with iCloud Photos, click Library in the sidebar, click Days in the toolbar, then click the Pause button at the bottom of the Days view. Photos pauses uploading and downloading for 24 hours and then resumes automatically.
You can have multiple photo libraries, but iCloud Photos keeps only the photos and videos in the System Photo Library up to date. See System Photo Library overview and Designate a library as the System Photo Library.
Stop using iCloud Photos on a Mac
You can turn off iCloud Photos on your Mac so that photos aren’t updated between your Mac and your other devices—for example, if you’re selling or giving away your Mac.
Important: If you turn off iCloud Photos, you’ll be prompted to select “Download Originals to this Mac” in the iCloud pane of Photos preferences so that all your original photos are automatically downloaded to your Mac. Be sure to allow time for your originals to download before turning off iCloud Photos. Once downloaded, your photos are safely stored in Photos where you can use them, but they are no longer transferred to your other devices.
In the Photos app
on your Mac, choose Photos > Preferences, then click iCloud.Deselect the iCloud Photos checkbox.
Click Download to download your photos in iCloud to your Mac, or click Remove from Mac to remove any photos and videos that have not been fully downloaded.
These items will still be available on your other devices that use iCloud.
After you turn off iCloud Photos, edits you make to photos on your Mac don’t appear on your other devices. New photos and videos from other Mac computers and devices aren’t transferred to your Mac. Your photo library remains in iCloud and available to other devices that use iCloud Photos.
If you don’t use iCloud Photos on your Mac, you can sync your Mac and a connected iPhone or iPad to transfer photos. See Sync photos between your Mac and iPhone or iPad.
Stop using iCloud Photos on all your computers and devices
You can stop using iCloud Photos on all your Mac computers and devices and no longer share any items between them.
On your Mac, open Apple ID preferences in System Preferences, then click iCloud in the sidebar.
Click the Manage button, click Photos, then click “Turn off and Delete.”
WARNING: If you turn off iCloud Photos on all your devices, your photos and videos will be deleted from iCloud in 30 days, and you won’t be able to recover them, unless you click Undo Delete before that time.