I want to know how to Dual boot windows 10 from Ubuntu 16.04 but I don't know how. I have a windows 10 flash drive to download it from.
Ubuntu recommends you install Windows first.
(This method does not work for computers with UEFI boot. In consequence, it won't work for pre-installed Windows 8 and some pre-installed with Windows 7.)
IF SOMETHING GOES WRONG?
Create a NTFS partition for Windows using Gparted
sudo apt install gparted)
MAKE SURE TO BACKUP THE MBR!
Install Windows normally
Then boot into a LIVECD (try ubuntu without installing)
We need the handy-dandy Gparted again.
Mount the root partition inside the LiveCD.
Then, restore the MBR.
Now setup the grub to boot windows. :)