ssh onto your pi, if you haven't enabled ssh, put the microSD back in the machine where you cut the immage file from, two disks will appear if its a Linux PC, one on Windows - it will be called boot. Get into the root directory of the microSD card and create a file - doesn't need any content, called ssh. On Linux simply use the command 'touch ssh'. Then eject the card and put it back in your pi.
Then ssh to it - putty is by far the best ssh client for Windows btw. its name will be octopi if you have the octopi image on the microSD or raspberrypi if its pretty much any other image. at the login prompt the username is pi and the password is raspberry.. That put you in the pi users home directory.
Then use the instructions from the Argon one case video.
In an nutshell, curl goes and gets the Argon code, then sends the argon1.sh file its just downloaded to the sh - shell command and installs it.. I've just tried to download it and the download is broken with an account suspended message, otherwise I'd have explained what its doing..
Does that help...?? BTW the demo video is showing installation on a Pi with a desktop, its not recommended to install the desktop on octopi - because it uses CPU better applied to managing your 3D printer.