debugging .asm file

When I want to debug my .asm file how do I do it line by line? Do I have to go into debug mode and enter the lines each one at a time? If that is the only way then how do I enter the labels in the code that I want to jump to at the debug prompt. When I enter labels it gives an error. for instance

Code:

; TESTQUAD.ASM: TEST MY PROGRAM
;
	.MODEL SMALL
	.DATA
X1 DB 4		;TEST CASE FOR VALUE 4
Y1 DW 10	                ; Y SHOULD BE 10
PASS DB 'Procedure passes.',0DH,0AH,'$'
FAIL DB 'Procedure fails.',0DH,0AH,'$'

	.CODE
	.STARTUP
	MOV AL,X1	;LOAD MY FIRST VALUE
	CALL QUAD	;COMPUTE RESULTS
	CMP AX,Y1 	;LOOK FOR MATCH
	JNZ BAD
	LEA DX,PASS	;SETUP POINTER
	JMP SEND	;OUTPUT MESSAGE
BAD: 	LEA DX,FAIL	;SETUP POINTER TO FAIL MESSAGE
SEND: 	MOV AH,9	;DISPLAY STRING FUNCTION
	INT 21H	;DOS CALL
	.EXIT

QUAD	PROC NEAR
	MOV BL,AL	;save a copy of input value
	MOV CX,10	;setting up 10x	
	MUL CX		;compute 10X
	MOV AL,32	; placing 50 dec into AL
	SUB AX,CX	; perform y=50-10x
	RET
QUAD	ENDP

END

if I enter SEND: it will give an error and I am still trying to get this to work.