This is very important, so it's worth taking a moment to give an example. If you have a window that you wish to drawing 5-pixel-wide solid (not dashed) lines in, and you want the ends of the line segments to be rounded, you might do:

     graphics_attributes(Window, [line_width(5), cap_style(round)])

That's all there is to it. You don't need to specify the line_style(solid) attribute, because this is the default. You may count on the defaults; they are often what you want anyway. It is perfectly possible to create a window and start drawing into it without setting any graphics attributes, because the defaults may be good enough.