@Jamesstaddon?
I wrote an article quite a while back about a totally different subject, but it somewhat addresses your question. Feel free to take a look at it here: https://www.lenspiration.com/forums/topic/easy-to-read-user-guide-for-youngno-yn-560-iii-speedlight/
The idea of “stops” is an important one when dealing with the exposure triangle. Each of the 3 parts of the triangle: (aperture, shutter speed, and ISO) affect the exposure the same way. i.e. When you change your ISO 1 stop higher, your photo will get brighter, just the same as decreasing your shutter speed 1 stop makes your photo brighter, and opening up your aperture 1 stop makes it brighter. Theoretically every one of those will affect the brightness of your image exactly the same. So it doesn’t matter which one you use to make your photo brighter, if you go 1 stop, your photo will get one 1 stop brighter.
What makes it interesting is that each part of the triangle not only affects exposure (brightness), but like you said, aperture affects DOF, shutter speed affects motion blur, and ISO can make your photo noisy if it’s pushed too far. So the tricky part of the exposure triangle is to balance out the 3 components till they do what you want them to do.
Let’s take a theoretical example that happens in real life quite often. Let’s say that I want to take a picture of a flower in the flower garden with my 50mm f/1.8 lens. My camera is set to Auto Mode, and it chooses these settings:
Shutter speed: 1/250
Aperture: f/5.6
ISO Speed: 200
I snap a picture, and the exposure is right on, not too bright, not too dark, just perfect. However, with the aperture set at f/5.6 the DOF is pretty large, and I don’t like how it’s trying to bring the nearby flowers into focus too. So I decide to change the DOF by adjusting my aperture value to f/2. Now remember, I already know what my picture should look like in terms of exposure. So I just need to keep my triangle balanced to achieve the same exposure with my new aperture setting of f/2.
Let’s switch our camera over to Manual Mode now, and plug in our settings that we have so far.
Shutter speed: 1/250
Aperture: f/2
ISO Speed: 200
If we snap a picture now, our photo will be WAY overexposed. We’ve messed with one point of the triangle, but failed to balance it out with the other 2 points.
Let’s do the math. f/5.6 to f/2 is 3 stops. f/2 -> f/2.8 -> f/4 -> f/5.6 So if we change just the aperture, our photo will be overexposed by 3 stops. To compensate, we need to adjust the other 2 points of the triangle, (shutter speed and aperture). Using the other 2 points, we need to darken the photo by 3 stops so that we have an even exposure again. So let’s adjust the ISO speed from 200 down to 100. That makes our photo 1 stop darker, but we need 3 altogether. So let’s adjust our shutter speed 2 stops. 1/250 -> 1/500 is 1 stop, and 1/500 -> 1/1000 is 2 stops. So our final settings should be as follows:
Shutter Speed: 1/1000
Aperture Value: f/2
ISO speed: 100
Now we’ve got our nice blurry background by changing the aperture, but we’ve balanced out the exposure so that it stays the same by using the other points of the triangle.
Hopefully that helps you out a little bit, feel free to ask if you’re still unsure about something!
Note that if you had used A/Av mode, instead of M Mode you could have just changed your aperture, and the camera would automatically have adjusted the other settings for you.
Also, most cameras allow you to change your exposure settings in 1/2 stops too, so you can get even finer control over the balance of the exposure triangle. (My Pentax camera allows me to change settings in 1/3 stops!)