There are really only three things that you need to learn to understand Photography. Once you understand these three basic elements, and how they relate to each other, you’ll only be limited by your own creativity and desire to practice. These things are:

Aperture : If you look into a DSLR lens, you’ll see a set of blades that form a hole in the middle to let light pass through. That hole is the Aperture, and the lens can move those blades to make the hole smaller or larger. The larger the hole, the more light gets through, obviously. Your camera’s aperture control, then, is another way to change how much light gets to the sensor. The size of the aperture controls how much of the image appears to be in focus behind and in front of what you’re focused on. This effect is Dept-Of-Field(DoF). When the background gets blurry very quickly as it gets further from the subject, we call it “shallow” depth of field. If most of the picture appears to be in focus, from near to far, we call it “deep” instead.

Shutter Speed : Shutter is simply a door to let light into a light-proof box where the sensor resides. Shutter Speed is the duration that the shutter is open, and as you’d expect, the longer it says open, the more light is able to get to the sensor. In simple words, you can control the motion of your subject with this.

ISO : If you have ever bought a film roll, you will recall that you had a choice of different types. In most stores, you could buy 100, 200 and 400 speed films, and in a good camera shop, you could buy many more than that. These numbers are the film’s ISO rating, sometimes called the film-speed (or before the 1990s, it was called the ASA). With film, the higher the number (eg, 400, 800, 1600), the more sensitive the film was to light, so it could be used in darker environments. The lower the number (eg, 50, 100, 200), the less sensitive to light it was, making it better suited to use in bright daylight. So why wouldn’t people just shoot ISO 1600 film all the time? Unfortunately, higher speed film was also more grainy and had duller colors. This phenomenon is known as “Digital Noise”.

Exposure - Working Together : To get a better grip on how these three elements work together to create a photograph, an analogy may be helpful. Think of it this way: taking a photograph is like filling a bucket with water from a hose. If you fill the bucket all the way but don’t overflow, we could say that we have a Correct Exposure. In photography, getting a correct exposure means that the right amount of light gets to the sensor for the ISO setting, creating a picture that is not too bright or too dark.

I intended to give you a general understanding of the three most important concepts in photography and their relationship to each other. Hope this helps you.

Let me know if you an in-depth explanation about these concepts.