First you need to select your line thickness from the drop list under Draw Lines icon. Then check the box for Vertex Line. You will also need to select a line colour (if not using the default red) before you start.
It is a little tricky to explain. You can always go to the EM-COP Collaboration on line training package to view a quick video.
Your cursor will now be a pencil icon so you can start. First move to the point on your Map View where you want to start your line - now click your mouse button. A dot will appear, now move your mouse to your next point. You will see the line drawing as you move. Once you get to the next point - click your mouse button. Keep repeating this process until you have drawn lines between all your points. Now double click your mouse button. This will end your line.
BUT you will need to click the Navigation button on the mapping toolbar
or press Esc on your keyboard to turn the draw vertex line function off.