The term for the sun going down over the horizon is "sunset." This occurs to the west due the counter-clockwise rotation of the Earth. Depending on the tilt of the Earth's axis, the sunset happens earlier in the winter and later in the summer in the northern hemisphere.
The southern hemisphere has the opposite experience with the sunset, where their sunsets occur earlier in the summer and later in the winter. Sometimes during a sunset the sun and sky look red and orange. This is due to the fact that it takes longer for the light to reach the Earth as the sun sets. When this happens the blue light waves in the color spectrum have already dispersed, leaving the red and orange light waves visible.