wat version of photoshop are you using?
...i dont even remember the basics steps to do the shading for anime...
adding the shading by of coz choosing a darker layer and the best is
by making another layer so that if happen you made a mistake you can
just delete the "darker layer" and build without have to delete the original
layer.
..well, ...i do know how to use pen-tool to draw the parts that needs shading... but when I press the ' fill path' button ...the path that should be coloured is not coloured while the parts that is not ..is fill with the colour instead...I know this is the consequence of wrong setting...what should i do to correct this? .. :?:
yes, there must a setting which let you invert your selection. meaning that
the area where you choose to "fill" is NOT "fill"
it must be in the area pen-tool...
please go to pen tool bar and can you see there are boxes beside the pen

maybe you have chosen the one which shown in the picture above. It actually inverted the area of your selection. Try meddling with the other
boxes and you will learn the effect.
..and when colouring the parts with paint bucket tool ..after you have apply the colour..do you people find that there are like..some tiny areas especially those at SHARP corners left out..uncoloured?
This is maybe bcoz of the tolerance strength you choose when trying to paint bucket the area. As you can see when you try to scan your picture
the color balance between the white paper and your line art are not the same in every area. Due to this when you try to paint bucket with a minimal tolerance strength, it will only select certain area. This application
same goes for "magic wand tool".
click the paint bucket tool bar--> can you see there are a lot of option
up on your image.
fill,pattern,mode,opacity,
tolerance,[anti-aliase,contiguas,all layers]
hope this will help u