Sunshine is the light that comes from the sun. On a clear, cloudless spring day, you can go outside and enjoy the sunshine.
Scientifically, sunshine or sunlight is the radiation that the sun gives off. You can describe any light or warmth you observe from the sun as sunshine: "Look at the sunshine sparkling on the lake this morning!" Figuratively, the word is also used for cheerfulness, warmth, and happiness: "It's all sunshine and sing-alongs in the kindergarten classroom, but fourth grade is totally different."