Formatting a disk means completely erasing it and preparing it for a new use. If you accidentally format a disk, whatever files or data were on the disk will be gone.

Formatting disks in Windows 95/98/Me/2000/XP
* Insert the disk
* Double click on My Computer
* Right-click on 3-1/2 floppy [A:] icon and choose Format (left-click it).
* Left-click once on the Start button
* Wait for the formatting process to finish and the drive light to go off before removing the disk.

Formatting disks in DOS
* Insert the disk
* Type format a: at the MS-DOS prompt.