are you talking about your builder brush, or a added/subtracted/mover brush? If you are not talking about your builder brush, then you must rebuild your map before you can see the changes that have been made. be sure you have the brush selected, to do this click on one of its vertexes. if the brush is selected. it will become brighter, and you will be able to see a + on the center point (unless you select one other than the center point). be sure you have the move button selected and are holding ctrl. thats all i can think of.