It is important that you expose your images as good as possible to achieve the best results. Even if you follow the 3 C’s of photography, those being Contrast, Content and Composition, a wrongly exposed picture wont look good. If you overexpose, you loose your highlights. If you underexpose you loos your shadows.
To alter your exposure, you have three parameters that you can change. They are: Aperture, also known as f stop, Shutter Speed and ISO.
The first setting to consider is your Aperture: Do you want a shallow depth of field or a deeper depth of field? A wide Aperture like f/1.4 or f/1.8 leads to a very blurry background, or a shallow dof, but also let’s in tons of light. A narrow Aperture like f/16 produces quite a deep dof, but also cuts down on the light entering your camera. I wont touch diffraction here, that’s a story for another time.
To compensate for your chosen Aperture or, again, for stylistic choice, you can then adjust your Shutter Speed. If you want to really freeze the action, you’ll need a faster Shutter Speed, with the Shutter Speed depending on the speed of your subject. If you are more into smoothly blurred water and skies, you need a real slow Shutter Speed.
In photography, you have the liberty to adjust your Aperture and Shutter Speed to your liking. But sometimes, the Shutter Speed range off your camera isn’t great enough. When your image would be underexposed, you have the ability to adjust your ISO. Just keep in mind that a higher ISO usually introduces more digital noise, or grain, into your picture.
When you are overexposed at Base ISO (usually around 100) but also don’t want to change your Aperture or, in the case of videography, have a fixed shutter speed, you can bring down the light using ND filters. I don’t have a great one, but it does it’s job. At least in video. For photography, it is just to weak.
If you shoot RAW, which I highly recommend by the way, you can ‘fake’ a higher ISO by playing with the Exposure values in Post. You can also adjust your highlights and shadows to be more equally exposed. But you can’t really change your Shutter Speed or Aperture after the fact. While you can certainly fake motion blur and a shallow depth of field, removing both is mostly impossible. So get your exposure right-ish in camera, and you will have an easier life during post processing.
I hope you can navigate your way through the Exposure Triangle now. It’s not as dangerous as the Bermuda Triangle:)