Aperture or your "f-stop" controls how much light is exposed to the camera's censor by making the opening larger or smaller as indicated in this diagram:
A lower f-stop such as f1.4 is a larger opening, meaning more light is being let into the camera. A higher f-stop such as f16 is a smaller opening meaning less light is being let into the camera. The lens included in this photography kit has an f-stop range of f3.5-f22.
You can adjust your aperture by using the black dial on the top of the camera to the right of the Mode dial. A lower f-stop is ideal for dark environments and a higher f-stop is ideal for bright environments to maintain a properly exposed image.
While Aperture impacts the exposure of your image, it also impacts its depth of field or the range within which the subjects in your image are in focus.
As indicated by the diagram, a lower f-stop (which brings in more light) also creates a shallow depth of field meaning subjects in the foreground will be in focus and subjects in the background will be blurred. This can make really appealing images if that is the desired effect.
The higher the f-stop the more deep your depth of field or focus becomes. For instance, at f22, the entirety of the image will be in focus. No blurring effect takes place.
What happens when you want to take a photo with a shallow depth of field, but the low f-stop makes the image overexposed or too bright?