Just note that if you choose to continue down this path, I am not responsible for any damage done to you, your computer(s), or your property. If you type any kind of error that NASM doesn't catch, anything could happen from your computer halting, to your CPU bursting into flames. A note of caution to any brave souls wanting to go this way.
Didn't fall asleep? Great! Now to prepare to write an os, do the following (if you can't do something, go to the next bullet point. If you CAN do something, do it and stop):
-get a floppy disk and create a file named boot.asm (in a temporary folder, you have to put this in the boot sector which I'll show you how to do it later). Set your bios to boot off the floppy disk (take the floppy out until you have some real code).
-if you know what grub is and how to port it to a cd, do it now. And also create boot.asm (do this in a temporary folder along with grub files until it is time to burn).
-set up a virtual machine. I recommend Microsoft virtual machine for this. Just note that you will need an empty flash drive, cd, or floppy to do this.
-Set up network booting. Good luck. I can only point you to google for this one. I could never get it working.
-scream. You might want to read some other articles on this site.