Understanding the fundamental concepts of photography
Photography is the art, science, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film.
The amount of light that reaches your camera sensor, controlled by ISO, aperture, and shutter speed.
The sharpness of your subject. You can control what's in focus and what's blurred.
How you arrange elements in your frame to create visually appealing images.