Small introduction to "zoom".
As you surely know "zoom" is the magnification and see something that is more or less closely.
You have, in theory, a mouse with a scroll wheel between the two buttons, well, after drawing something, just a line, try to rotate slowly in one direction and another with the mouse wheel.
You will see items you have drawn closer until it disappears from the screen or leave up to a certain point and then stop.
Note also, for example, after drawing a line, the difference to use the "zoom wheel" after you move the pointer near one end or the other of the line.
You'll see that the design approaches and moves away relative to the position of the pointer, and then to an area of design that you have freely given with the mouse, in this case at one end of a line.
We therefore have a dual function that allows us to approach or move away from the objects and to move in any direction on the design, moving away from a point and reconnecting to another.
We'll see after other commands specific to the "zoom".