The freehand line tool
Using the freehand line tool is a lot like drawing with a regular pen on paper.
If you are using a mouse, click and then move the mouse while keeping the button pressed.
If a line you have drawn is just slightly off from where you want it to be, you can use the hand tool to adjust it. But if you are way off it might be easier to just click the undo button and try again.
You have the option of drawing a solid or a dashed line. The type of line used can be selected using the controls located to the right of the tool bar.