Inner (bright) angle (_cone)
The angle, in inches, in which cone is full-lit. It works separately from outer angle, so you can use either both or one of those keyvalues.
Outer (fading) angle (_cone2)
The angle, in inches, in which cone is fading out (outside of inner angle). It works separately from inner angle, so you can use either both or one of those keyvalues.
Pitch determines direction of the light, '0' is horizontal, '90' is vertical from top, '-90' is vertical from bottom. You can use an info_null as a light target instead.
Entity to Point At (target)
The light will point at this target.
Is Sky (_sky)
Makes light_spot simulates a light_environment, it will emit light from all sky textures.
First three integer numbers are the color (RGB). The fourth number is the brightness.