Here you'll learn the three basic parts to an exposure, and why you'd want to change the settings of each one even if it will give your image the same exact brightness. 

 

Aperture - This is like the iris of the lens. The larger the aperture, the more light gets let into the camera. The smaller, the less. It gets a bit confusing here because f numbers, or fstops for larger apertures are actually the lower numbers (ex. f1.4 lets in more light than f5.6, etc). The other effect caused by different apertures is that larger apertures have a shallower depth of field (how much is in focus, think blurry backgrounds). While most of us love photos with a nice blurred out background, some times you actually want more to be in focus, and so you have to use a smaller aperture. (it's actually more complicated than that, as the focal length of the lens, and your camera to subject distance plays a large role too, more on that later). Here is what you need to know: Full F stops, meaning, when you go from one to the next, you are letting either twice as much light into the camera, or half as much. 

F1.4 > F2.0 > F2.8 > F4.0 > F5.6 > F8 > F11 > F16 > F22

 

**any number in between these is a partial stop, and depending on how your camera set, it will either be in 1/3 incriments, or 1/2

 

Now... to the easier stuff

Shutter Speed - this is how long the camera lets light in to take the picture. Yep...that's it...but... most of the time we want sharp photos, and when you are not using a tripod, or have a moving subject, or... your hands are shakey, you will need to use a faster shutter speed to 'freeze' the motion. For anything that moves, even slowly, MY personal rule is no slower than 1/200 of a second. That isn't even enough some times. If something is moving quickly you might want to use 1/500 as a starting point. Some times, that isn't enough (like for most sports) and you'll want to be at a minimum of 1/1000. If you are photographing still objects and have good hands, the general rule for an adequately sharp photo is 1/(whatever the focal length you are using, if using a full frame camera. Multiply the focal length by 1.6 for crop sensors). That almost never works for me though, so I do 1/twice the focal length. 

 

ISO - This is the easiest of the three parts to exposure. Your ISO is a setting that dictates how sensitive the camera is to light (or how much the camera will boost the signal that the sensor receives). Most cameras start at ISO 100 as their lowest setting. If you double or half the ISO values, you are either increasing the brightness by one stop, or reducing it by one stop, respectively. For simplicity's sake, here is a list of FULL stops in ISO. Anything in between is either a 1/3 or 2/3 stop. 

 

ISO 100, 200, 400, 800, 1600, 3200, 6400, etc.

 

What you need to know here is that it's best to keep your ISO at the lowest value that you can in a given situation, because the higher that value, the more grain you will have in your photos (and color loss, and dynamic range loss aka the amount of detail in shadow and bright/highlight areas of the photo). You only raise the ISO if you cannot get a good enough shutter speed for whatever you're photographing, or if you want to use a smaller aperture to get more in focus (since you will be lessening the amount of light entering the camera). 

Some examples where you would use higher ISO's outdoors despite bright light: Let's say you're shooting outdoor sports and want to freeze action, so you want to use a shutter speed of 1/1000 or faster. Some times, to get that shutter speed, you will have to boost the ISO (if you already are using the largest aperture, and can't get that shutter speed that is, or you want to purposely use a smaller aperture to get more in focus).