This is an overview. If it feels a bit overwhelming, that is normal. You do not need to remember every detail of this. For now. Over the next lessons we will look into each of the complex systems that make up the exposure triangle in more detail. And then things will make more sense. However, sometimes it's good to know where you're going.

The exposure triangle is a way to explain how your shutter, your aperture, and the ISO work together to yield exposure. Exposure deals with the general brightness, or darkness, of your photo. A photo is properly exposed when it's neither too dark or too bright.
Too dark would be lacking definition in the shadow areas. Too bright would be having highlights so bright that they all turn white.

All 3 of the complex systems making up the exposure triangle can be used independently of each other to make your photo brighter or darker. But there are side effects. And it is these side effects that we want for artistic purposes.

The shutter controls the light entering the camera as well as how blurry a photo might be. We'll take a really good look in classes 7 and 8.

The aperture controls the light entering the camera as well as how fuzzy the background gets. We'll have to look at your lens too, and we'll do that in classes 9 through 12.

The ISO controls how sensitive your camera is to light. At higher ISO settings you may see some noise in your photo. How that works we'll look at in class 13.

And what you'd do with all that is in classes 14, and 16 through 18.

The thing though:
You can use any of the 3 to make your photo brighter or darker, independently of each other. However, you can't take a photo without having all 3 involved. It is that fact that sometimes seems to make mastering your camera such a confusing battle.

The exposure applies to the whole image area. You can have only one exposure per photo. Having a different exposure on your subject than on the background would be neat, but that's not how things work.

For you to practice:
See if you can find any photos that are bright or dark. Look at them and try to see why you feel that way.