The “Drag and Drop” feature is one of the very useful features in SharePoint Online and On Premise SharePoint. You can use this to drag and drop files from SharePoint Document Libraries or from Windows Folders.
Drag Files from Windows Explorer to a Library
Choose a folder from explorer and choose a Doc Library in SharePoint and drag and drop the files as needed.

Drag Files from Doc Library to a Library
Choose a file/folders from one doc library in SharePoint and drag and drop the files as shown here.

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