I am also a newbie at linux and have been for nearly 20 years! lol. it’s ok.
I haven;t looked at the quick start guide you refer to, instead I am referencing knowledge obtained a few years ago, for setting up a different SBC in headless mode (not important but it was a Banana Pi R1 router board, with IPFire iamge, that had no hdmi drivers, so could only use a ttl-usb adaptor)
if you google “jetsonhacks uart ttl” you’ll find a video guide that he’s created for connecting to the serial port on the nano.
once connected to that port with a usb-ttl cable (as mentioned, I have an arduino that I have used in the past for this purpose but cannot remember off the top of my head, if it is happy to play at 3.3v or if it is 5v, so it might be better to purchase a dedicated cable rather than using an arduino. I did that because I had one available and no other reason) you can use putty to connect to the serial port and it will be similar to having a screen connected. I suspect that you’ll be presented with the text version of the initial startup scripts (choosing username, location/timezone,password etc) but this is guesswork on my part as I haven’t actually tried it. My arduino is actually in storage in my mothers loft, over 100 miles away
I will read the quick start guide and see if I can make sense of the problem you are having but I am unable to reboot to windows currently as I am attempting to recompile the kernel on my laptop, to get my own SD Card reader to work.
I have had a look at that guide. like I said, I believe my nano 4gb dev kit presents itself as an ethernet adaptor rather than a serial com device. It could be a difference in the way the boards/SD card image is configured, it could be a guide for an older version of the image OR it could be that I am mistaken (it has certainly happened before)
However, the usb-ttl cable method should still work even if I am incorrect about windows seeing my device as a network device. I only plugged it in the one time, on the day I purchased it, out of curiosity. But I am sure I remember correctly ssh’ing into it - but this was after going through the initial setup using a keyboard and monitor