Basically, it is there to let you know, or prompt you that the computer is waiting for your input, waiting for you to tell it what to do. After you have typed a command at the prompt you have to press the enter key to let the computer know that you are done telling it what to do and that it should now act on your instructions. If you make a mistake in typing your command, you will get an error message and a new prompt. You will need to retype your command correctly to make the computer act. This is a very fundamental way to interact with a computer and if you understand it you will better understand any other operating system such as Windows 3.1, Windows 95, Windows NT, Unix and even Macintosh.
Next lets take a look at the disk drive designations and the file structure .
All drive designations are represented by a letter and a colon. In fact, if you only have one floppy disk drive either letter will work. Usually that is the only drive letter associated with the hard disk drive. Try putting the floppy back in the floppy disk drive and try again. If you look at the front of the computer as you press the enter key, you will see a light come on on the floppy disk drive as the computer tries to access it.