virtualbox.org

How to install windose 10 on Virtual box through the USB flash drive?

If you mean that you have to a "Win10 installation USB disk" and you would like to install that in a VirtualBox VM, I don't think it's going to be that easy:

• If you want to boot from a USB in VirtualBox, you've got to change the settings to boot from EFI. Only EFI supports booting from a USB, not BIOS. And EFI was mostly created to support OSX hosts and it is still listed as experimental. Of course it's getting better support and it will be improving over time.
• You've got to create a VMDK file that points to the raw USB and make that your boot device.
• Since that file will point to the raw filesystem, chances are that you have to be an administrator of the computer.
• I haven't tried it, neither do I know anyone that has. I could try it later, if I have some time, just to see if it works.

Your best bet at this point is to create an ISO from that USB and use that. Search for "how to".