Shutter speed is a fun one that you can get creative with but it can also be very limiting in the beginning. Just know that it is easier to understand than aperture but harder to deal with. Shutter speed affects the time it takes for the photo to capture.
Its main purpose is to control exposure. Exposure is how much light is exposed to the sensor, or film. The shutter speed is the metric that determines how fast the shutter moves. It is measured in seconds or fractions of a second. You can read it as 1/1000 in camera, on my analog camera however it goes from 1 - 1000 but again those are fractions not seconds.
How this impacts exposure. The longer it takes, closer you get to whole numbers, the more light is let in. So the longer it takes to close the shutter the brighter the exposure will be. Closer to whole numbers is raising exposure the smaller fractions get is lowering the exposure.
Raising exposure: 1/1000 —--> 1/100
Lowering the exposure: 1/100 —--> 1/1000
Unfortunately, the longer it takes the more motion can occur. So if you have shaky hands like me a general rule of thumb is don’t go below 1/100 because the camera movement will translate into motion blur. And you will have really shaky photos.
If it helps think of it as a clap. Look at a moving subject and clap once quickly. From the moment your hands start to move to the moment you clap is the amount of light that is let in. Looking at the moving subject clap once again but slowly. Notice how much it moves between the moment you start moving your hands and the moment you clap. Your hands are the shutter.
Back to the camera, now that you know how shutter speed works you can see how it affects the other aspects of the exposure triangle. When you change one you change them all. So if you want to take a long exposure or take sports photos you will be using a different shutter speed. A long exposure is for when you want to capitalize on the effects of prolonged lighting. Some examples are: light painting, astrophotography, and motion blur intentional photos like water falls. With these you will have to close off or lower your aperture or ISO. Sports photography normally means less motion blur. So, you have to adjust for a shorter shutter speed time with aperture and ISO by raising the exposure.
If you want a fun activity to practice change your camera to shutter speed priority and notice how it affects your photos appearance outside of exposure. Then take a mental note of how the camera changes aperture and ISO to accommodate the change in shutter speed. Take photos of moving objects or while moving to really understand how shutter speed is changing the aesthetics of your photography.
Get to shooting!