What does color temperature mean?
Put simply, color temperature is a measurement of the hue of the light sources influencing your shot. Color temperature is measured in degrees Kelvin. The lower the Kelvin setting in the camera, the bluer (or colder) your light sources appear, while the higher the Kelvin, the more orange (or hotter) they will seem. This is the first level of color correction before post-production is even reached, and it all falls under the umbrella of a process of color balancing your image called White Balancing. (Source: Film Draft)
This video will show you how to export your video from iMovie to share it with the world. Confused by size settings? This video will clear that up for you!