Choose a brush from the Brush Presets picker, and set brush options. (See Select a preset brush.)

Choose a blending mode from the Mode menu. (See About blending modes.)

Choose an option from the Style menu to control the shape of the paint stroke.

For Area, enter a value to specify the area covered by the paint strokes. The greater the size, the larger the covered area and the more numerous the strokes.

For Tolerance, enter a value to limit the regions where paint strokes can be applied. A low tolerance lets you paint unlimited strokes anywhere in the image. A high tolerance limits paint strokes to areas that differ considerably from the color in the source state or snapshot.