Ubuntu dual booting Dell laptop with preloaded windows

First of all we need to download the original dell windows .iso image from dell official website, as a precaution in case of something goes wrong

Download using Dell recovery tool
https://www.dell.com/support/home/us/en/04/drivers/osiso/recoverytool/
https://www.dell.com/support/article/us/en/04/sln301761/how-to-use-the-dell-hosted-recovery-image-of-linux?lang=en#Issue3
Keep this iso image burned in DVD or a bootable USB separately
You can use this link for more details about downloading pre-installed  Operating system.

You need to check harddisk partition scheme, it should be GPT, almost all the preloaded windows OS are installed in UEFI mode.
- Right click "This PC" -> "Manage" -> "Disk management"
- Right click on hard disk (on windows installed hard disk, in case of more than one hdd installed)
- Click "volumes" on new opened box. Now you can see the partitioning scheme (I already installed Ubuntu, its swap and root partitions are also shown in below diagram)

- We need to create some unallocated hard disk space to install Ubuntu

In machine/laptop BIOS setup,
- Turn off secure boot (Recent Ubuntu versions are compatible with secure boot)
- Use AHCI as disk mode
- Disable fastboot in windows OS

You need to have Ubuntu, Linux Mint or any other linux variation to use as the dual booting OS.
I use Rufus to make my USB bootable. Alternatively Unetbooting also works, but YUMI multiboot did not work in my machine.

Make the USB bootable in UEFI mode if your machine has GPT, else make it BIOS if partitioning scheme is MBR

After creating the linux bootable USB restart the machine, boot the usb drive. You should choose "Try Ubuntu without Installing" option.

Wait till Ubuntu live session starts.

If your machine has nvidia  graphics it may show a black screen and shows nothing. To solve that problem you can refer this post

Then open "gparted" program and verify that same disk partition scheme is shown in Ubuntu also. (Disk sizes may shown slightly different, but the partition order should be same). And the unallocated hdd space should also shown.

If you just see only an unallocated partition in "gparted" there is something wrong. Please verify that you use same GPT or MBR partition scheme in windows OS and Ubuntu image. Don't proceed with installation

Now you are ready to go with installation. Exit "gparted" and click on "Install Ubuntu to Hard disk" on desktop. Proceed with installation. You will see your windows installation is automatically detected by Ubuntu setup