Zooming means to move "closer to" or "farther from" the drawing space, viewing the drawing at a greater or smaller level of detail.
You can always check the current zoom percentage via the zoom indicator, located, by default, at the lower right corner of the screen.

Using a Wheel Mouse

Zooming with a wheel mouse is a particularly handy way to get around in a drawing. Move the cursor to where you want to work, and move the wheel backward to zoom out or forward to zoom in.
Some wheel mouse setups require that the scroll bars be turned off for zooming to work.
Some wheel mice are set up by default to scroll instead of zoom. If you would like your wheel to zoom, select Tools / Customize and open the Intellimouse page. You will be able to assign commands to the wheel functions. This feature works with other wheel mice as well.

Zoom In and Zoom Out

Hotkey: <+> or <-> (on numeric keypad)
                                         
Magnifies or shrinks the current view. The zoom factor is equal to two by default, but you can change this in the Advanced Preferences page of the Program Setup.

Tip: Change the zoom factor to 1.4 to double the view every two zoom steps.

If you zoom using the <+> and <-> keys of the numeric keypad, the view centers on the cursor. If you use the View menu commands or icons, the zoom will center on the current view, regardless of the position of the cursor.

Note: As you zoom out, the representation of small objects is simplified, thereby increasing redraw speed. You can set the size at which this occurs using the Suppress display field on the Display page of the Drawing Setup.

 Zoom Window

Hotkey: Ctrl+Home
                    
Zooms to an area defined by a rectangle. The rectangle is defined by selecting its two opposite corners, or by dragging the mouse from one corner to the other.

Note: Because the dimensions of the zoom rectangle will probably not be exactly proportional to the screen, the closest view that includes the entire rectangle will be used.

Zoom Extents

Hotkey: Ctrl+Backspace
                    
Zooms to an area that completely contains all visible objects (including lights and camera objects). This is the same area enclosed by the selection rectangle if you select all the objects. Any objects on an invisible layer will not be taken into consideration.

Zoom Full View

Hotkey: Shift+Backspace
                     
Only available in Paper Space, displays the entire drawing sheet. The drawing sheet may consist of multiple printer paper sheets, indicated by dashed lines.

 Zoom Selection

Hotkey: Alt+Backspace
                     
Zooms to an area that completely contains all currently selected objects.

Tip: You can also use the Design Director to quickly zoom on an object or group of objects. For a single object, see Design Director-Graphics. For a group of objects, see Design Director-Categories.

Printed Size

                   
Zooms at approximately the size the drawing will be when printed. In this view, one inch of screen space is approximately equal to one inch on paper. The exact ratio of screen space to Paper Space will vary, depending on your graphics display and screen resolution.

Uniform for All Views

Used for multiple windows of the same drawing, enables you to zoom all windows simultaneously.