Help is used to access the information and help file from a MS-DOS prompt.

MS-DOS 5.x uses help.exe.
MS-DOS 6.x uses help.com.
Microsoft Windows 2000 uses help.exe
Microsoft Windows XP uses help.exe

For quick reference help with MS-DOS commands in any of the versions of MS-DOS or Windows you can also use the -help or /? after a command for example

dir -help
or
dir /?

APPEND	ARP	ASSOC	AT	ATTRIB	BREAK	CACLS	CALL	CD
CHCP	CHDIR	CHKDSK	CHKNTFS	CLS	CMD	COLOR	COMMAND	COMP
COMPACT	CONTROL	CONVERT	COPY	DATE	DEBUG	DEL	DELTREE	DIR 2
DIR ...	DISKCOMP	DISKCOPY	DOSKEY	ECHO	EDIT	EDLIN	ERASE	EXIT
EXPAND	FC	FDISK	FIND	FOR	FORMAT	FTP	GRAFTABL	HELP
IPCONFIG	LABEL	LOADFIX	MD	MEM	MKDIR	MODE	MORE	MOVE
MSCDEX	NBTSTAT	NET	NETSTAT	NLSFUNC	NSLOOKUP	PATH	PATHPING	PAUSE
PING	PRINT	PROMPT	RD	REN	RENAME	RMDIR	ROUTE	SET
SETVER	SHARE	SHUTDOWN	SORT	SUBST	TIME	TREE	TYPE	UNLOCK
VER	VERIFY	VOL	XCOPY