As hatstead says, we really need more information from you to be able to help. But, from what you have said, I am guessing that you have the Contiguous box unchecked in the tool options. So, if you are trying to color a black and white drawing, if you click anywhere in the white area of the image, the entire page will be colored with the Paint Bucket. If you check the contiguous box, the color will be limited to the contiguous pixels of the same color where you click. See my screenshot below for the difference. If this is not the case, then we definitely need more information from you.