You should create an installation/LiveUSB from .iso file as it simplifies installation process.
See official Installation/FromUSBStick.
After booting from USB you will be presented the same interface as if you have booted from a LiveCD/DVD.
You could try installing Ubuntu in a VM first so this will leave your current Win 8 installation without change.
A VM (virtual machine) installation is just a file (set of files) on any existing partition/drive.
If you install Ubuntu natively you need at least 2 new partitions and there will be some common boot manager (GRUB or Windows boot manager) which has to be configured to boot both OSs.
For native Ubuntu installation you have to check if current Windows 8 installation is on MBR or GPT style disk. There are different guides for BIOS/MBR and for UEFI/GPT installation/dual-booting.