The sun is a sphere. It has a diameter of 32 miles and is located approximately 3000 miles above the surface of the earth.
The Sun's area of light is limited to a circular area of light upon the earth much like the light of a lighthouse is limited to a finite circular area around it. The rotating light on a lighthouse does not propagate infinitely into the distance. This means that only certain portions of the Earth are lightened at a time. It also describes how night and day arise on the Flat Earth. The apparent view of rising and setting are caused by perspective, just as a flock of birds overhead will descend into the horizon as it flies into the distance.
Rendered picture of the Sun in relation to the Earth
Temperature Variations of sunlight
Magnification of the Sun at Sunset, or how the sun maintains its size throughout the day.