DOS normally comes on several floppies. They are labelled sequentially, from 1 to the number of floppies in the set. In addition, the installation procedure requires that these floppies be used in order, using the first one to start a "SETUP" program, and waiting until the program requests the next disk. At this time, the disk present in the drive will be removed, and replaced with the next disk in the set. A key will be pressed to indicate to the setup program that the disk has been inserted, at which point it will continue copying files until the next disk.
In short: you can make a basic DOS boot disk with one floppy, but it's necessary to use several to install the whole OS on a computer. Ideally, of course, using the installation program. (for DOS versions 4 and higher)