Do not be afraid of the terminal. Often easy to just copy & paste a command, just be sure source of command is reliable.
If you do not have live installer flash drive.
And install:
Updated to 24.04
Bitlocker in Windows, turn off so installer can correctly see drive
https://documentation.ubuntu.com/desktop/en/latest/tutorial/install-ubuntu-desktop/
My lsblk as an example, that we need to see from your system
> fred@dell5310:~$ lsblk -e 7 -o MODEL,NAME,FSTYPE,LABEL,MOUNTPOINT,SIZE,fsused
> MODEL NAME FSTYPE LABEL MOUNTPOIN SIZE FSUSED
> PC SN530 NVMe WDC 512GB nvme0n1 476.9G
> ├─nvme0n1p1 vfat ESP /boot/efi 200M 127.3M
> ├─nvme0n1p2 128M
> ├─nvme0n1p3 ntfs OS 202.4G
> ├─nvme0n1p4 vfat FAT32 6G
> ├─nvme0n1p5 ntfs Shared 63.9G
> ├─nvme0n1p6 ext4 noble-dell / 39.1G 17.5G
> ├─nvme0n1p7 ext4 data-dell /mnt/data 142.6G 87.5G
> ├─nvme0n1p8 swap 4.1G
> ├─nvme0n1p9 ntfs WINRETOOLS 1.4G
> ├─nvme0n1p10 ntfs Image 15.7G
> └─nvme0n1p11 ntfs DELLSUPPORT 1.4G
One site on Windows fast startup off. There also may be an UEFI/BIOS setting for fast boot which also should be off as that assumes no system changes and always default boots previous configuration.
http://www.tenforums.com/tutorials/4189-fast-startup-turn-off-windows-10-a.html