Aperture is a zipper that stands over the lens. When the blender opens, it passes light into the camera. If the blister opens more, more light enters the camera. If it opens less, less light comes in.
On most digital cameras, the f-number moves somewhere between 2 and 22, although a larger range is possible. If f is number 2, this means that the blend is completely open. If it is 22, this means that the blend is almost completely closed, and that very little light enters the device.
Why is the aperture important? If you take pictures in an ambient where the lighting is poor (say, at dusk, or indoors), you need a larger aperture to allow more light to enter the camera. If you take pictures in an ambient where the light is extremely strong (desert at the floor), you need a small aperture, otherwise the light will enter the camera.
Each lens has its own focal length. The focal length is the physical property of the lens, and it represents the distance between the lens and the point where the light beams that have passed through that lens. The lens in the camera is not a lens, but a lens system. Simplicity works, it is usually viewed as one lens.
What’s the depth of sharpness?
Imagine that you are at a world-class bazaar and colorful objects, and want to take pictures of a person. A big chance is that the face of this person will inevitably be drowned in a bunch of backgrounds. However, you want to emphasize on it to separate the face from the background. This is best achieved if the face is perfectly sharp on the photo, and the background is blurred.
Or, for example, you want to paint a building, but in front of it are some containers, parked cars or something similar that you do not want in a photo. In this case, you want the construction (which is located in the other plan) to be sharp, and the car and containers (which are in the foreground) are blurred. If you take a picture of a range of objects located at different distances from you, depth sharpness allows you to extract some of them. Those objects that are in the field of depth of sharpness will be sharp, while the others will be blurred.