makefile problem

[nikhil d purwant]

hi people 

     so i got a good answer to my question about makefile the other day thanks the concerned people. now can anybody please explain me following lines from the makefile i have i know it has to do something with 
the ipmlicit rules but i'm not being able to figure out exactly what it is (the CFLAGS LINE)
 
appending the part of the makefile 

----------------------------------------------------------------------
INCLUDEDIR =some path

#CFLAGS = -D__KERNEL__ -DMODULE  -DDEBUG_MESSAGE -DDEBUG_CRUDE -O -I$(INCLUDEDIR)
CFLAGS = -D__KERNEL__ -DMODULE  -O -I$(INCLUDEDIR)

CC= gcc

arrg.o:
	   $(CC) -c $(CFLAGS) arrg.c

----------------------------------------------------------------------


also any pointers to understand modules and loading them and unloading them etc. 



thanks in advance 

                                                -nikhil