Only a small portion of the electomagnetic spectrum of wavelengths is visible to the human eye. That portion of the electomagnetic spectrum can be imaged because the cornea and the lens of the eye can bend the path of light rays onto the retina, the back surface detector. An image is formed upside down on the retinal rods and cones nerve endings that are light senitive. These nerve endings produce signals that are sent along optical nerve fibers to be processed by vision centers of the brain. The brain interprets the world as right side up. In essence, the rods and cones convert light energy into thousands of data bits called nerve pulses. These pulses are transfered to the brain by cables called nerves. The signal pulses are processed by the brain into an understandable image.
This how the disk of the Sun would look in visible light. DO NOT look directly at the Sun!