Installing a Fresh Distro on Oryx Pro
Once you've got the USB stick in the computer, reboot your system. You’ll need to tell the computer to boot from the live disk by holding F7 or F1 source.
If you're NOT going with Pop_OS, you'll likely need to install System76 drivers and the appropriate NVIDIA drivers. More info on this here.
Some System76/Pop!_OS Links
Installing System76 and appropriate NVIDIA drivers for System76 machine