A DMG file is a disk image file used by macOS to distribute and install software. It is a compressed file that contains the installation package for a particular software, in this case, Apple Configurator. The DMG file is used to install the Apple Configurator application on a Mac, which can then be used to configure and manage Apple devices.
Note: Apple Configurator is distributed exclusively through the Mac App Store as an installer package inside a .dmg -like download process. There is no standalone .dmg file available outside the App Store. apple configurator dmg file link