Points

When this button is on, a rectangular brush is used to
change the color or glyph of points that are contained by
the brush.

Lines

When this button is on, a crosshair brush is used to change
the color of line segments.  If either the horizontal or
vertical arm of the crosshair intersects a line segments, it
will be brushed.

If both Points and Lines are on, then both point and line
brushing are done at the same time.