Perspective in photography refers to the relationship between the objects in an image; determined by an object's relative position, size, scale and space. The world we live in is three-dimensional whereas photographs are two-dimensional representations of that world.
The focal length and the distance to the subject will create a certain perspective. By changing the focal length and distance to the subject, the perspective can be changed dramatically.
The most effective way to alter the perspective in photography is to change the vantage point. It is a fact the most common way to take an image is from eye level. If you move to the left or right, kneel down or find a higher point to shoot the image from, the perspective will change. Just a few feet might have great impact on the composition. As soon you have learned about the importance of composition in photography you will start looking for other camera positions. These aspects are especially important in Commercial Real Estate, Landscape, and Street Photography.
Distance is most often manipulated by the use of different lenses. A wide-angle lens will cause the linear perspective to be over emphasized, while a long telephoto will reduce the sense of distance. Lenses allow you to do is framing the shot successfully from a viewpoint that gives you the preferred perspective.
Below are some examples of images I have taken that exhibit different perspectives and vantage points, and how altering these two things can effectively change how photographs are viewed.