The direction of the light. With a zero rotation, the light illuminates horizontally in world space in the -Z direction. A negative x/pitch angle makes the light point downward as the sun would in daylight. In that case, an object with identity transform (looking forward in the z direction), would have its shadow cast behind it, and decrementing the y/yaw angle would make it rotate clockwise (as seen from a top-down view). The z/roll angle has no effect.
The intensity of the directional light.
The color of the directional light.