The file is located in
Program Files/Oracle/VirtualBox/VBoxManage.exe and is used as a command-line interface with VirtualBox.
I'm using it to convert the .vdi image to a .vdmk (for VMware).
Here's an example script:
$ VBoxManage list hdds
But where do I run this command? In Windows cmd? I tried both in cmd and in Linux but I can't figure it out.