By default, Vagrant will share your project directory (the directory with the Vagrantfile) to /vagrant.
If you need to add other folders, then you can to specify them in a Vagrantfile this way:
config.vm.synced_folder "~/", "/media/psf/Home" config.vm.synced_folder "/", "/media/psf/Mac_Root"
You might want to share folders by passing Parallels Command Line as described in Customization with prlctl, but it won't work. It is done to avoid conflicts and keep vagrant configs more platform agnostic.
You can read more about syncing host and guest folders in the Vagrant Documentation.