Angle of view
Focal length of your Lens effects the angle of view. If you move towards the higher number or the longer focal length you get a narrow angle of view and in effect cover a more distant area. As you decrease the focal length that is, move towards a smaller number or use a shorter focal length, you start covering a wider angle of view. This is why a longer focal length is known as a Telephoto lens and a shorter one is known as a wide angle lens.