Aperture and Shutter Speed

When we combine aperture and shutter speed together, then we have "Exposure".
The correct aperture and shutter speed dictates how well the photo will be. A good photo needs the right about of light. The right amount of light is done thought the correct setting of the aperture and the amount of time we let the light coming through.
Aperture is the hole where we let the light through in the camera. The larger aperture number makes the smaller the aperture opening, and the smaller the aperture makes the larger aperture opening. The aperture size dictates how much light is let into the camera at a fix period of time.

Use a tap to fill a bucket of water as an example. Let’s say to take a perfect exposed photo is like to fill a bucket of water, then aperture will be the size of the tap, and the amount of water flowing out of the tap will depend on how much we open up the tap. So if I were to open the aperture to 2, then the volume of water will be huge. Filling the bucket of water may take only 5 sec. If over 5 sec, the bucket will over flow, and there is too much light. Then it will cause "over exposure" on the photo, and the photos will show lots of "white". If less then 5 sec, the bucket will not be full, and the photo will be under exposure. The photo will appear dark.

If I were to close the aperture down to 11, similarly with a smaller tap, the flow of water will be significantly smaller. It will take longer to fill up the bucket. It may take 10 sec. With the same logic, if over 10 sec, the photo will be over exposed. On the contrary, exposure time less then 10sec will cause the photo to be under exposed.