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That's not the Pen/Bezier tool. That the Node tool that you have selected in the screenshot. You have to use the Pen or Pencil tool to draw a line, then you have to switch to the Node to to adjust the lines. You can't draw with the Node tool.....well, not directly anyway.
I'm not sure if you made the Inskcape window very small, so it would all show up in the screenshot, or if your drawing with it that small. If you look at the bottom of the toolbar, the same bar where you have the Node tool selected, you'll see a tiny double arrow that looks like this only smaller: >> . If you click on that button, a little menu shows up showing you the rest of the tools. Or if you were to maximize the Inkscape window, you could see the Pen/Bezier tool button. It looks like this:
If you look in my forum signature, there are links to some really good manuals and tutorials. I would recommend the Quick Guide
