Solid Rectangle Tool
The Solid Rectangle tool draws filled-in rectangles.
To use this tool...
Once you have selected the colours you wish to use, click on the Solid Rectangle button and point the upper-left corner of the cursor where you want to place one of the rectangle's corners. Hold down the left mouse button to draw with the foreground colour, hold down the right mouse button to draw with the background colour. Drag the cursor to the opposite corner of the rectangle and release the mouse button.