Download files and folders from iCloud Drive
To download a file from iCloud Drive, either open the file or click the download button 
next to its name. When you download a folder, everything in that folder also downloads.
Download photos and videos from iCloud Photos
In Photos, double-click the photo or video to view it individually. The high-resolution version of that photo or video automatically downloads from iCloud Photos.
Download email attachments
Open the email message, then click the download icon 
for the attachment. If you don't see a download icon, the attachment is already downloaded.
Download your purchased movies and TV shows
Apple TV and iTunes also offer a download button for redownloading your purchased content. Learn how to redownload apps, music, movies, TV shows, and books.
Learn more
After you download a file, folder, movie, TV show, photo, email attachment, or video, Optimized Storage keeps it on your Mac until more storage space is needed.