Simply explained, Aperture is the opening through which light enters the optical system and falls on camera sensor. In other words, aperture controls the amount of light that falls on camera sensor. Aperture can be compared to our eyes that open wider in low light condition to let more light enter inside and similarly become narrower or smaller in bright light so as to block extra light from entering inside.
The diameter of an aperture is measured in f-stops. A lower f-stop number (say f/1.8) opens the aperture so that more light can come inside. Also, wide aperture results in sharpness of light rays with the right focal length only. Now what the hell does this mean? It simply means that here the main subject will be in focus while background will be blurred. This is the concept of 'Depth of Field' which i'll take up in another post.
Similarly, higher f-stop number (say f/11) will result in narrow aperture that will allow lesser light to pass. Narrower the aperture, sharper will be the background in your image. Note that I am talking about background here, main subject should always be in good focus.
Confusing ??? Start experimenting and things will be clearer. Also, don't forget to google and go through some more tutorials to get your fundas right.
