Why is photography so important?

Photography is important because it enables the diffusion of objective information through the visual capture of things as they really are. It allows people to accurately familiarize themselves with far-off landscapes and cultures. It also has the power to sway public opinion through the presentation of emotionally moving images.

How did photography become art?

In 1885, an art movement called Pictorialisim began, where a photographer would manipulate photographs with chemicals to change the way they looked. however, the public desired photographs that were sharply focused, and the movement ended in 1920. Stieglitz was a large contributor during those times and lobbied his position through his work. finally in 1924, the collection of 27 of his photographs, recognizing photography as a major artistic medium.
photography became an art largely due to the efforts of Alfred Stieglitz. in the early 20th century, Stieglitz used his influenced to bolster support that photography was an art, which eventually led to him being the first photographer featured in a museum.

What is the purpose of photography?

Photography is part of the evolution of human desire to capture and express life; since the earliest days of artistic expression and documentation in the form of cave painting, humans have been attempting to capture and record life around themselves in various formats, including drawing,painting,sculpturing,writing and photographing.
The question of photography ultimate purpose in many ways a deeply philosophical question,though the easy response can be seen in the ways people use cameras and what they choose as their subjects. since cameras became widely available in the 1990's, people have been capturing still images of their lives by photographing  their families, the places they visit, the things that are important to them and even themselves.