So every great photograph, or every photograph in general, have a proper exposure. And the proper exposure is pretty obvious. It's just making sure everything, whatever your subject is, is lit well.
There are three ways you can control your exposure. It's basically a balance of these three equations. It's your ISO, which is your grain quality. It's the overall quality of your image. Your shutter speed, which is how fast the shutter is opening and closing, exposing the sensor in your camera behind it. And your aperture, which is how wide the opening in your lens is, how much light it's letting in.
If we're shooting, let's say, at an ISO of 400, which is a very standard ISO. It was a very popular film speed back in the day before digital. And these days it's a very popular outdoor ISO. Let's say you're shooting at ISO 400 and you're shooting at f/2.8, so very open amount of space in your lens, a lot of light coming in. And you're shooting at 1/500th of a second. And that's the correct exposure.
Let's say I'm taking a picture of my dog outside. I like the way my dog looks but I want to get more of the background in focus. What can I do to do that? Well, I can bring my F-stop up to a higher F-stop and give it more depth of field. The smaller the opening in your lens, the more things will be in focus in the frame.
So let's say we bring it up to f/5.6. Well, if you look at your F-stop scale again, it's f/2.8, f/4, f/5.6. So we're going up two stops. That means we need to adjust either the ISO or the shutter speed accordingly to make it the same exposure.
Now, what we could do is we could take it, this down one stop to 1/250th and bring this up one stop to ISO 800. This will be the same exact exposure. Let's say that f/5.6 isn't cutting it and we want to go, have even more depth of field. We want to go up to f/8 to one more stop. It'd be the same thing. We can bring this down one more, we can bring that down one more. So we bring this down to 1/125th, keep this at 800. Again, it's the same thing.
So just a matter of knowing that first exposure and doing the math in your head to adjust accordingly each way. ISO, as you go up you're letting more light in. Aperture, as you go up you're letting less light in. Shutter speed, as you go up you're letting less light in. (?) keep in mind.
And that's the basics of exposure.