Clicking on the button
changess the cursor to an eye cursor.
The right mouse button wil anchor a rubber band at the current cursor position. Any further right click will draw a permanent marker line over the rubber band.
The rubber band will then be anchored again to the current cursor position.
To end the route mode, just click the button
again.
See also: How to edit the current route.
See also: How to execute the current route.