I'm trying to learn to use bezier tool to trace images and drawing, but it is not easy to control. However I noticed that end nodes cannot be changed into smooth as the others. Does it exist a way to do that?. Can someone help me?. There's an attached image to explain what I mean.

Hold shift-key down while dragging from that node.

More info here: http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Paths.html