请教关于makefile的问题

我是个初学者，对linux很感兴趣但是学起来很头痛，特别是关于makefile文件


# Comment/uncomment the following line to disable/enable debugging
#DEBUG = y

# This Makefile has been simplified as much as possible, by putting all
# generic material, independent of this specific directory, into
# ../Rules.make. Read that file for details
TOPDIR  := $(shell cd ..; pwd)
include $(TOPDIR)/Rules.make
# Add your debugging flag (or not) to CFLAGS
ifeq ($(DEBUG),y)
  DEBFLAGS = -O -g -DSCULL_DEBUG # "-O" is needed to expand inlines
else
  DEBFLAGS = -O2
endif
CFLAGS += $(DEBFLAGS)
CFLAGS += -I..
TARGET = scull
OBJS = $(TARGET).o
SRC = main.c pipe.c access.c
all: .depend $(TARGET).o        

$(TARGET).o: $(SRC:.c=.o)
$(LD) -r $^ -o $@
install:
install -d $(INSTALLDIR)
install -c $(TARGET).o $(INSTALLDIR)
clean:
rm -f *.o *~ core .depend
depend .depend dep:
$(CC) $(CFLAGS) -M *.c > $@

ifeq (.depend,$(wildcard .depend))
include .depend
endif
有几处看不太懂
1 all: .depend $(TARGET).o       据说makefile是从这里开始执行的，但是不知
   
depend .depend dep:
$(CC) $(CFLAGS) -M *.c > $@
是什么意思
2 这是个编译驱动模块的makefile它和编译一般的应用程序有什么区别啊　　　　　　

怎么没有人回啊，