The Brush tool and the Pencil tool paint the current foreground color on an image. The Brush tool creates soft strokes of color. The Pencil tool creates hard-edged lines.
Drag in the image to paint.
To draw a straight line, click a starting point in the image. Then hold down Shift, and click an ending point.
When using the Brush tool as an airbrush, hold down the mouse button without dragging to build up color.