Written by Nick Otter.
Create a hard drive partition (size >= 25GB) using Disk Management (walkthrough).
If after installing Ubuntu, you boot directly in Windows, check in UEFI settings for changing the boot order. If you see no option to set the boot to Ubuntu, you need to fix it from within Windows. When you are in Windows desktop, hover the mouse in left corner, right click and select administrator's command prompt. Then run the following command:
bcdedit /set "{bootmgr}" path \EFI\ubuntu\grubx64.efi
This should make the Grub (Linux boot agent) default and hence you can access both Ubuntu and Windows from it.
(Thanks itsfoss).
Thanks. This was written by Nick Otter.