How do I access the iCloud Drive window?

Yes, if you drag and drop or otherwise save or move files to the iCloud Drive folder on your Mac they will automatically sync with iCloud.

There will still be a local copy on your Mac in that iCloud Drive folder. The exception to that is if your Mac is low on storage and you have the Optimize Mac Storage option turned on in Apple menu > System Settings or System Preferences.

In the Finder "Go" menu click "iCloud Drive."

Or in the iCloud section of the Finder sidebar click "iCloud Drive." If it isn't in the Finder sidebar, go to Finder Settings (or Finder Preferences, click Sidebar at the top of the Settings window and put a checkmark in front of iCloud Drive.

Open Mac spotlight , and type iCloud Drive , click on enter key it will open Search with Spotlight on Mac - Apple Support