Many camera users today only use automation and point&shoot without any concern about what the automation is doing, or should be doing. However automation cannot recognize the scene nor its photographic needs. That requires a human brain and a few seconds of thinking about the situation. So only the easy pictures have much chance to come out right.
Learning exposure is the beginning skill you need to acquire about photography, and if you don't understand about choosing camera settings yet, you may want to look into it. Camera settings have much capability for even the difficult pictures, which automation can not handle (any difficult situations are generally impossible for the automation). Automation is very handy, since we don't have to know anything or to think about it (and we likely won’t even know what the settings used were), but then that only result is whatever the automation does. Except automation has no brain, and needs human help to recognize the situation to choose better choices for the specific scene.
“Exposure” is NOT just about how dark or light the picture is. Exposure is about using the right settings to get the best picture, like by freezing the subject motion or intentionally blurring it (waterfalls maybe). Or by stopping down aperture to increase the depth of field, or shooting wide open intentionally blur away the objectionable background. Or how do we make an acceptable portrait under a shade tree but with a bright sun background? Or indoors with a bright window behind? Situations vary, and need different techniques. That is photography, it is more than just a cell phone.
There are many creative choices possible in photography, which does require an adjustable camera, and some basics, and most of all, a few seconds of thought about the situation and what we are doing about it. But it’s all easy, and is the first thing photographers must learn. It’s fun getting it right, and soon becomes our automatic procedure, so that we just already know when we walk up to the scene. The brain is the photographers best tool, but knowing a few basics is a huge help too.
Choosing WHAT to point the camera at is a different discussion, but a photo scene allows a wide choice of possible Equivalent Exposure combinations, all “correct” with regard to exposure (even our cell phone must select one), but generally, only one is "right" or "best". The big advantage of using our human brain is that it can immediately recognize the subject and the situation, and can choose the best choice for this particular picture (and automation cannot). Exposure does NOT mean just exposure (not too dark, not too bright). It means choosing the best available exposure combination for the scene situation. If we consciously think a second about what we’re doing when we actually LOOK at the scene, our brain learns to likely “just know” immediately what it needs. Unless of course, you can't be bothered to think about what you're doing. 😊
Shown here is an example of one row from the EV Chart showing sample values chosen to be a normal bright direct sunlight level (called EV 15). For example one exposure combination for this EV 15 is f/4 at 1/2000 second (freezes motion). Or f/22 at 1/60 (much depth of field, but bad for motion). We can choose what is needed. All entries on this entire row are Equivalent Exposures. Equivalent means that all of them are a “correct” exposure (for the example light level), but we’re looking for the one best combination for our specific situation. Our brain is the best tool in photography, it sees and knows things at a glance, and it can help the camera, if we choose to use it. This is the fun in photography for many of us, to create the photo ourselves, to be the way we want it. Experiment a bit, it is the first step of understanding.
I am speaking of using camera A mode (Aperture Preferred), which likely is most commonly used, or maybe S mode (Shutter Preferred). We start by simply entering one reasonable number choice for the situation, and the camera meter selects the other number matching the exposure. So these can still be automation controlling the actual exposure, but we can choose the settings to use. When you’re aware you’re supposed to actually LOOK at the scene, you will have a pretty good idea about the situation when you first walk up. Before you click the shutter, you should have decided what f/stop, shutter speed and ISO combination is to be used, as the best choice for this subject situation. In most cases, this is not difficult, and soon we will be able to “just know” at a glance what is necessary. Your camera meter will first pick one combination with a correct exposure, but maybe another different combination is the best choice for this particular photo situation. You start by entering one of the numbers, usually aperture, and the camera meter determines the other one. Then you decide if those are the best numbers you can do for this situation. So we change it first if something else is better. Actually give it a try. You may not know yet how easy and satisfactory this is, but a very little experience will work wonders for you.
Exposure is determined by the combination of aperture, shutter speed and ISO. If you increase one of the three, you have to decrease the effect of one or both of the other two to keep the same Equivalent Exposure. In lessons, this combination is usually called “the Exposure Triangle”, just meaning these are the three factors of exposure (it is a good search term, but there is no actual triangle). We just take an instant to consider if this first metered combination is appropriate for the situation.
A light meter can only measure the brightness of a blob of light, but cannot recognize the scene or its needs. So the decisions about the scene situation require a human, with eyes and brain, which can analyze and understand. So remember, a fully automatic camera simply doesn’t know, and couldn’t care less. For one example, if there is a bright sun background behind a subject in the shade, the meter doesn’t have a chance without help. Just give a quick thought to what you’re doing, because that’s what makes the magic happen. This hobby gives joy in the results when you know how to get it right.
You set the aperture and the camera mode A meter figures out the shutter speed. That is automation too, but then our human brain can decide which combination is best, based on concerns other than literal exposure. We are Not so much selecting specific numbers, it’s more a hunch, generally just evaluating the obvious need for More shutter speed or More Depth of Field (or the best compromise of those). To allow that, sometimes we may need to increase ISO, or make some other compromise. Sometimes “all we can do” has to be the answer (but which is still our best choice). But when no problem factors are present, then choosing an aperture two or three stops up from maximum aperture is often a good general purpose choice (for generally good sharpness and depth, but still check the shutter speed).
It is a learning experience, and you will continue learning for years, but a little experience works wonders, and most cases are obvious and easy. The camera first meters the scene, and then we might change one of the three factors to be better for some specific reason. Then the camera meter gives us the resulting exposure combination, which we can consider again, to make sure. We looked at the scene and know what it needs. The meter is certainly a big help, but do give a thought to what you’re doing before you press the shutter button. This is easy, and soon you might not always even realize you’re doing it automatically. Like checking your car’s side mirror before changing lanes. You simply just glance at it, and the extra little bit of thought can dramatically improve the results of the situation. Try this a few times, it becomes easy and automatic.
The f/stop number is about the diameter of the lens aperture, which is how much light it lets in (a smaller f/stop number is a larger diameter aperture allowing more light, however a larger f/stop number is up to a point, generally sharper, creating more depth of field). Shutter speed is the time duration while the shutter is open, letting light in (a faster shutter stops motion better, but which reduces the exposure, which can be offset by opening aperture or increasing ISO). ISO is the sensitivity to light, how well the light registers on the sensor (a higher ISO is more sensitive to dim light, but which often adds greater digital noise). The choice and balance of these three factors is all important to photography.
We don't actually compute motion blur or depth of field numbers for each picture, instead we just learn that action pictures need a faster shutter speed (or a speedlight flash). Or that some pictures need more depth of field, stopping down aperture or using a shorter focal length is all that is possible. These two ideas can conflict about exposure however, and what is possible becomes important, meaning we still have to make all three factors of shutter speed, f/stop, and ISO combine to match the correct exposure (use of Equivalent Exposures). This becomes easy and second nature with a little experience. It does mean we have to think a bit about what we're doing, but we can usually "just know", and then we simply do what is necessary as an automatic reflex. We just know what to do (because we have experience thinking about things before).
There is much online about learning Exposure