exposure
Exposure is the amount of light per unit area.This is determined by just 3 camera settings : aperture, shutter speed and ISO.
#1 aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane.
Diagram of decreasing aperture sizes (increasing f-numbers) for "full stop" increments (factor of two aperture area per stop)
#2 shutter speed
The length of time a camera's shutter is open when taking a photograph. The amount of light that reaches the film or image sensor is proportional to the exposure time.
#3 ISO
> The measure of a photographic film's sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system. A closely related ISO system is used to measure the sensitivity of digital imaging systems.
> The lower the ISO number, the less sensitive it is to the light, while a higher ISO number increases the sensitivity of your camera.
> The lower the ISO number, the less sensitive it is to the light, while a higher ISO number increases the sensitivity of your camera.
composition
Composition is the placement or arrangement of visual elements or ingredients in a work of art, as distinct from the subject of a work.
Rule of third
A "rule of thumb" or guideline which applies to the process of composing visual images such as designs, films, paintings, and photographs.
Depth of field
The distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image.