Looks like you're trying to use Linux commands in Windows. "-f elf" will produce a linkable object file - whatever OS Nasm is running on - but the object format won't be right for Windows. Windows uses a varient of the COFF (common object file format) - "-f win32". (Nasm's "-f coff" is a different kind of COFF) There *is* a port of the linker "ld" to Windows, but it sounds like you haven't got it - or haven't got it installed right. Maybe available on the prof's computer, but not yours? You can get the Windows "ld" (and more) with the MinGW package, or the Cygwin package. Google for 'em if just ".org" doesn't work - probably will.
Better yet, install Linux, and "-f elf" and "ld" will work great!!!
Best,
Frank