Apple’s iCloud Drive lets you securely access all of your documents from your Mac, iPhone, iPad, iPod touch and even a Windows PC. There are various ways you can access the files:
When you add your Desktop and Documents to iCloud Drive, all of your files move to iCloud. On your Mac, you can find the files on your Desktop and in your Documents folder in Finder under iCloud. If you add a second Mac Desktop, you'll find those files in the Desktop folder in iCloud Drive. A folder is created with the same name as your second Mac.
(This how-to is based on my experiences and info on Apple's support pages — where the images sometimes come from.)