Your camera makes a lot of important calculations for you, and knowing what is going on enables to you take up where your camera leaves off.
One of the most important things your camera does is to make its best guess about how much light will be required to make the picture look good. There are two adjustments the camera can make in its attempt to accomplish this.
One is to decide how long the shutter will stay open. The shutter blocks the light when it is closed. While it is open light can reach the sensor that records the image. In the old days the image was recorded on film.
The other variable is something known to geeks to as the f/stop. There is a diaphragm that opens wider or less wide to control how much light reaches the sensor in any given amount of time. Let’s say your shutter speed is 1/100th of a second. At f/4 the sensor sees twice as much light as at the next setting, f/5.6. Each f/stop admits half as much or twice as much light as its neighbors.
Depending on your camera model, you might be able to choose these settings yourself. One of the incentives for doing that is that you might be photographing an activity where people are moving. You will want to opt for the faster shutter speed to stop the motion.
Another important consideration is called depth of field. Let’s say you are photographing a choir, and there are three rows of people. As the number representing f/stop gets bigger the range of focus increases. That can matter to you when you want sharpness front-to-back in a photograph.
Many cameras have a little dial with labels such as Auto, P, and M. My tiny Canon PowerShot A630 offers a dozen variations on this one dial. One of them enables the camera to record video. Another favors large lens openings to blur the background in portraits.
It will reward you to study the controls most relevant to the style of photography you enjoy. You have plenty of choices in this regard.