[Stiglr]

The Poly Line tool is very simple and straightforward. I'd be very surprised it isn't detailed completely in the User Guide. However, onward....

Hold your cursor over the Poly Line icon, and a small dialog will appear, telling you how to use it and how to "finish" a shape: click the Poly Line icon, then in one of the viewports click at consecutive points which describe the shape you want to draw; after you click to draw the last point, (not ON the last point) click with the center or right mousebutton and that completes the shape. (Even if you do end up with two vertices at the "end" of the shape, you can later select both vertices in Vertice mode, then do a Snap Together, followed by Weld, to be sure that they become one, single vertice)

After you draw your shape, it should be a simple matter to make a surface of it: in Vertice Mode, select all the vertices and either create an Ordered Surface or create Convex Object/Hull. Which one you use probably depends on whether you selected all the vertices in consecutive order, such that the surfaces will draw correctly. Also, if the vertices describe a shape with 3 dimensions instead of 2 (and thus has depth) you may have to use Convex Object/Hull, otherwise you'll get some really problematic surfaces, "black" surfaces, etc.

After you make the surface, you can do anything else you want: extrude, indent, bevel, etc.