Hi and welcome.
Virtual windows on apple soft, is that even allowed these days.
Generally if you are to use VBox, the way to get it to work,
1. Create a new virtual drive and settings. Here I would recommend and absolute minimum of 250GB disk space 8-16 GB of ram and use whatever grahics (min 4GB) and sound the thing uses.
2. Start the virtual drive and give it aminute or two so the new drive gets built into the system.
3. Insert whatever media you are going to use to install the Windows software. Best way would be to download the Windows 10 iso from the Microsft site and then either make a bootable dvd of it or a bootable USB stick, whichever you need.
4 installing the media i would use the new drives boot key usually F8 while the machine is loading and point it at the media you are using.
5 follow on screen instructions.
Windows 10 is now out of End of Life warranty and has no updates left to download. You MAY be able to get the extended security download still for free.
Any issues please feel free to come back to us or PM me and ill be glad to help.