Something else that might help is indenting your code. It makes code easier to read and makes it easier to tell where things begin and end:
@LOOP
FOR X=0 TO 15 STEP 1
FOR Y=15 TO 0 STEP -1
COLOR X,Y:PRINT "HELLO WORLD"
NEXT
NEXT
GOTO @LOOP
3そうだね 未プレイ