Single-point perspective** adds depth to an image. The effect can be subtle or obvious, depending on how you shoot the picture and what else is going on in the scene. The classic example of single-point perspective is a railroad track going into the distance, the two lines seemingly getting closer together as they are receed in the background.
To get the lines-coming-together effect, position your camera at a 90 degree angle to two (or more) straight lines. While most straight lines end at some point before they would appear to merge, if you were to draw lines continuing them, the lines would merge.