From the link you post, look like you have to follow the step. 1) click "create the dos start disk", then default select the " using dos system files locate at" , 2) you may need to select the files where they are. 3) click the start.
You must have MS-DOS installed to make a DOS startup disk. If you don't have DOS installed, you should install it (on your computer or on another computer). If you have got an old machine (386, 486 or something like that) you could take all the files in floppy disks and then when you put in one floppy you copy the files on the HDD; on the same floppy you copy more files; and so on. If you have a CD-ROM drive it would be better, you would not need to copy the files on a hard drive, you would just select it from the CD and you should be ready to go on.