Ubuntu VM is part of Windows 10 and both systems share the same resources (e.g. the file system). You access your Ubuntu on Windows via a command prompt, pretty much similar to DOS command prompt.
And to answer your question: you need to activate this feature on Windows and then run a quick installation procedure to set it up - the whole thing takes less than 5 minutes.
Thanks very much! Setting this up today! Your post has saved me a bunch of hassle setting up dual booting ubuntu, thank you!!!