This tutorial only applies to old Macs that have a regular 1.4MB floppy disk drive, NOT a 800KB or 400KB floppy drive.  800KB/400KB floppy drives were uniquely manufactured by Apple and cannot be emulated using a generic PC floppy drive at all, because they have special firmware in their boards that can pack more DATA per track than regular PC drives could, at the time.  Moreover, please note that even if you have a Mac floppy drive but that it is USB attached, it will NOT make 800KB/400KB floppies.  In a nutshell, to make 800KB/400KB floppies, you absolutely need a beige Mac from the 90's with an internal floppy drive, sorry.

Now if you're here to make a 1.4MB install/boot disk for your Mac, this should work on any computer that has a regular 1.4MB floppy drive.

For Windows instructions, read this excellent tutorial by Terry Stewart: https://www.classic-computers.org.nz/blog/2011-12-29-disk-from-images-mac.htm

For Mac OS X instructions, read the following excellent tutorial by Paul Brierley.  If you're in a hurry, you can directly skip to the last big paragraph named "A Step by Step Guide" here: https://lowendmac.com/2008/creating-classic-mac-boot-floppies-in-os-x/

[ ! ] Note: Under modern macOS, you will need to unmount the floppy disk drive before you can copy to it using Terminal.  Run this command before you start following further instructions: sudo diskutil unmount /dev/disk3 (where "disk3" is your floppy drive, make sure this is correct by checking with the sudo df -h command)

[ ! ] Note 2: "skip=1" command parameter is ONLY good for DiskCopy (.img) images.  If you are cloning a DiskDup+ (.dsk) image, DO NOT put "skip=1" in your command line.