[UbuntuGnome] Installing as a Dual Boot with Windows 10

On the instructions I found for doing this on your website there is section that says normal install,you are supposed to
turn off secure boot .
3 times I have tried to install Ubuntu 18.04 LTS but the section normal install,you are supposed to turn off secure boot does not appear .So it wants to use the whole disk,and I never get to section Install Ubuntu alongside Windows Boot.

How do I Install Ubuntu alongside Windows Boot??