When you change focal lengths by zooming the lens, two important effects are immediately obvious in the lens' angle of view and its magnifying power.
Angle of view refers to how much of a scene the lens covers.
Zoomed out using a shorter focal lenth, you have a wide-angle of view that captures a wide expanse of a scene. As you zoom in using a longer focal length, the field of view narrows and you can isolate small portions of the scene without moving closer to the subject. Here you see the angle of view of various focal length lenses. The shorter focal length lenses are on the left and the longer ones on the right. Magnification is related to the lens' angle of view.