If this icon is selected then you can drag a guideline to a new position by clicking on it with the left mouse button and holding this down while moving it to where you want it. If you hold down a [Shift] key while clicking on the line, it will be copied rather than moved.
The following procedure is recommended:
Set one vertical and one horizontal guideline. After this switch to the
Move mode and copy all further required guidelines by
dragging them out from the existing ones while holding down the
[Shift] key. This will save you a lot of needless clicking on the
A second click on this icon switches off the Move mode.