This command will create a new Line. It can have several different angles/routes in the same line, e.g. alongside a river. You can click on the map to create a node of the new line. When you do this a flag icon will be added to the map. The base of the flag orange icon represents the position of the first added node. As you continue to click, further nodes will be added. Last added node will have black pushpin icon.
When you have drawn the line with the required shape you can then click the Finish button on the tool bar to complete it. Also there is no fill style used as the polyline is being drawn which allows you to distinguish it from a polygon.