Video: Copy or move library files by using Open with Explorer
This video shows how to open a library on a SharePoint site in File Explorer and then drag multiple files to a library on another site. First, we show how to do this when you have all the latest software. Then we show an alternate way to do this when you have previous versions—for example Windows 7, Office 2010, and Internet Explorer 9.
In OneDrive for Business, you may need to click Settings > Show Ribbon to show the Library tab.
For additional help with Open with Explorer, see Troubleshoot the 'Open with Explorer' command in Microsoft SharePoint Online in Microsoft Office 365 or search the Office 365 Community forums.