Access your iCloud content on your Mac
iCloud is the easiest way to make sure all your important content is everywhere you are. iCloud stores your documents, photos, music, apps, contacts, and calendars, so you can access them anytime you’re connected to the web.
You can use your Apple ID to set up a free iCloud account, which comes with 5 GB of free storage space. Purchases you make from the iTunes Store, App Store, or Apple Books don’t count toward your available space.
iCloud keeps everything up to date on your devices. So if you have an iPhone, iPad, or iPod touch, just sign in to iCloud using the same Apple ID and you’ll have everything you need.
For system requirements about devices that support iCloud, see the Apple Support article System requirements for iCloud.
Here are some of the things you can do with iCloud.
Automatically store your desktop and Documents folder in iCloud Drive. You can save files in your Documents folder or on your desktop, and they’re automatically available on iCloud Drive and accessible wherever you are. When working with iCloud Drive, you have access to files on your MacBook Air, on your iPhone or iPad in the Files app, on the web at iCloud.com, or on a Windows PC in the iCloud app. When you make changes to a file on a device or on iCloud Drive, you’ll see your edits wherever you view the file.
To get started, click the System Preferences icon 
in the Dock, click iCloud, select iCloud Drive, click Options, then select “Desktop & Documents Folders.” To learn more, see the Apple Support article Add your Desktop and Documents files to iCloud Drive.
Share purchases and storage with Family Sharing. Up to six members of your family can share their purchases from the iTunes Store, App Store, and Apple Books and share the same storage plan—even if they each use their own iCloud account. Pay for family purchases with one credit card, and approve kids’ spending right from your MacBook Air or iOS device. Also share photos, a family calendar, reminders, and locations. To set up Family Sharing if you didn’t when you set up your Mac, click the System Preferences icon in the Dock, click iCloud, then click Set Up Family. To learn more, see the Apple Support article Set up Family Sharing.
Store and share photos using iCloud Photos and Shared Albums. Store your photo library in iCloud and see your photos and videos, as well as the edits you make to them, on all your devices. Share photos and videos with only the people you choose, and let them add their own photos, videos, and comments. To get started, click the System Preferences icon in the Dock, click iCloud, select Photos, then click Options. To learn more, see the Apple Support article Set up and use iCloud Photos.
Enjoy your purchases anywhere. When you’re signed in to iCloud, purchases you’ve made on the iTunes Store, App Store, and Apple Books are available at any time, no matter which computer or device you used to purchase them. So all your music, movies, books, and more are available wherever you go.
Locate your MacBook Air with Find My Mac. If your MacBook Air is missing, you can easily locate it on a map, lock its screen, or even erase its data remotely if you have Find My Mac turned on. To turn on Find My Mac, click the System Preferences icon in the Dock, click iCloud, then click Find My Mac. See the Apple Support article If your Mac is lost or stolen.
Learn more. See What is iCloud? in the macOS User Guide.