As others have stated there are much better guides than this.

I did this recently for fun, including the bootloader (I considered GRUB cheating!) The best tutorial IMO was https://samypesse.gitbook.io/how-to-create-an-operating-syst...

Some other useful resources I found:

  - http://3zanders.co.uk/2017/10/13/writing-a-bootloader/
  - http://mikeos.sourceforge.net/write-your-own-os.html
  - https://www.nasm.us/doc/
  - http://faydoc.tripod.com/cpu/
  - https://github.com/cfenollosa/os-tutorialjos