When you set the shutter speed to a higher value, it means that you are taking a picture FASTER. To explain why it is darker, realize that there is a sensor behind the shutter and the longer the sensor sees light, the brighter the picture will be. Similarly, the sensor is not exposed to a lot of light when you set it to a high shutter speed.
ISO is the sensitivity of the camera's sensor to light. The higher the ISO, the more grain/noise there is in your picture, but you will be able to shoot at faster shutter speeds because the ISO compensates for the less amount of light your sensor is exposed to. When you set it to a low ISO, you will have less grain/noise but you will have to decrease the shutter speed in order to expose your sensor to more light.
Aperture is the opening of your lens. If the lens has a small aperture (I.e. a high F value - f/8), less light will come through the lens and consequently, the sensor will be exposed to less light. Thus, making your pictures darker (in comparison to a low F stop). A high F value also leads to a sharper picture (i.e a deeper depth of field). For landscapes, a good rule of thumb is shooting with f/8. When you shoot with a lower value of aperture, the lens opening is larger. You are allowing more light into your camera and will make the picture brighter. A small F value will lead to a shallow depth of field. It is a good idea to use a smaller value for portraits and for low-light situations.
In short,
↑ shutter speed, darker picture
↓ shutter speed, brighter picture
↑ ISO, brighter picture
↓ ISO, darker picture
↑ Aperture, darker picture
↓ Aperture, brighter picture
Anh-Viet
