Changes the horizontal space between selected .

Make Equal

Moves the selected objects so that there is equal space between them using the outermost objects as endpoints. The outermost objects do not move.

Toolbar shortcut: toolbar button.

Increase

Increases horizontal spacing by one grid unit based on the object with focus. When an object has focus, white handles appear on its borders. You can change the size of your grid units in the General tab of the Options dialog box.

Toolbar shortcut: toolbar button.

Decrease

Decreases horizontal spacing by one grid unit based on the object with focus. When an object has focus, white handles appear on its borders. You can change the size of your grid units in the General tab of the Options dialog box.

Toolbar shortcut: toolbar button.

Remove

Removes the horizontal space so that the objects are aligned with their edges touching based on the object with focus. When an object has focus, white handles appear on its borders.

Toolbar shortcut: toolbar button.

Note
The object with focus does not move but the other objects move around it.
Note
If using the Horizontal Spacing command does not produce the results you want, try to manually rearrange some of the objects and repeat the command. Also, try the using the Vertical Spacing command.