Eraser
Eraser Tool
This tool is useful for erasing parts of the design. Click and drag through the area you want to erase. Note, however, that it works by marking areas of a layer as being transparent. This may result in a checkerboard pattern being shown. This pattern is simply used to indicate areas of the design that are transparent -- it is not actually part of the design.
This tool is also useful while working with multiple layers. If you have portions of a layer that you want to show through to the top layers, you can use the eraser tool on those top layers. You can also use the eraser to return the affected area to a state selected in the History palette.
Original design(left), an area been erased by Eraser Tool(right)