You're welcome NickyT.
It's probably not worth your while getting too bogged down in the names of things.
You want a connected sequence of line segments, some of which may be straight, some of which may be curved.
Some applications call them polylines, some (like Scribus) call them bezier curves. There are also B-splines (which I remember from my old CAD days), NURBS (generally used in 3D modelling) and many others.
They're pretty much the same thing but the main difference is generally how they are constructed. Most applications have different construction tools but there's not much anyone can do about that.
Technical purists will probably have some argument with that but basically, for creating pages in Scribus, a bezier curve is a polyline and a polyline is a bezier curve. What they're called is fairly irrelevant. (Call them "wibbly wobbly things" if it helps!) The main thing is to just use whatever tool does the job and don't think too much about what the tool is called.
For complicated drawings I would recommend using Inkscape instead of Scribus and then importing the Inkscape SVG into Scribus. Inkscape gives you much better control over what you're drawing and the tools are more refined. On the other hand, the tools in Scribus are just fine for most people's needs and you don't need to keep going over to another application and re-importing after changes.
The main illustration on this
http://forums.scribus.net/index.php/topic,1855.0.html was created entirely using Scribus bezier curves so it can do more than the basic stuff but it becomes tiresome after a while. Use whichever application/tool that works best for you in the circumstances you find yourself in.