An article with all the details is over at Computer Hope --- http://www.computerhope.com/issues/ch000425.htm
Did you just inherit an older computer with Windows 98 on it? (And is it Windows 98 original or Windows 98 2nd Edition? [It will be printed on the Windows CD ... Ah- do you have a Windows 98/98se CD?]
If this is an inherited machine, are you sure what operating system (if any) is installed on the hard drive? [A Windows 98 bootable floppy diskette will boot almost any PC to the command prompt: but it doesn't mean that Windows 98 is installed on that computer. To see if a Windows 95/98/98se/Me operating system is installed, rather than typing "win" from the C:> command prompt, type "dir". If you see a long list of directories, then at least you have found out that the hard drive is using a Windows 95/98/98se/Me compatible file system (either FAT16 or FAT32 - don't worry if this doesn't make sense at the moment). Windows 2000 and Windows XP can also use that file system.
If you see no directories at all listed when you type in the "dir" command, the hard drive is either blank, or is formatted for use with a non-Windows 95/98/98se/Me file system. It could be formatted with the file system that Windows 2000 and Windows XP use = NTFS (New Technology File System). Windows 95/98/98se/Me cannot read NTFS. The hard drive could also be formatted for other operating systems, such as Unix, Linux, OS/2, etc.
I imagine you might have more questions - let us know what answers you need.
Best of luck
. . . Gary