Coloring a Sketch with Gimp

I am trying to color a pic from a manga with gimp and i have been through a few of the tutorials. There are two things that i cannot get to work. The first thing is making the sketch "multiply." Apparently this allows me to make it so the black in the sketch is always on top and color on other layers will be seen with the sketch. The second thing is actually coloring it in! I am not sure how to use a color with either the paintbrush or the airbrush. However, the paintbrush will do white or black but i cant choose a color. The airbush just seems to not work well or something. It wont really color it just puts spots of the drawing.

I already know about gimptalk but i couldnt find what i needed there.

sounds like ur completely new to gimp...

okay for the first to get the layer to multiply i'm assuming u will need the make the duplicate of ur first layer... then just press Shift+L and the layers box will come up.. there u can duplicate the layer then change it to multiply by goin to the box with should say "normal". just press the arrow pointing down next to it and u can change it to multiply.

and to change colours u just need to double click on the black or white colour box. then u can choose ur colour from there.

hope that helps.. sorry if my explanations aren't clear.

ty for the help you have provided, i got the colors to work just fine. However, the method you used to multiply does not seem to work. I followed your directions and i was able to color the plain white background behind the sketch. It seems that the colors are not coming through the white parts of the sketch. instead of having only black on top, it is the whole sketch. I thought that doing this would allow me to color on multiple layers, having the color come through to the top and the black parts of the sketch would remain as well.