What is the best way to cover this shaped cake with fondant?
Same way you cover any other cake in fondant? It is just like a square, only it has two more corners. And I find squares easier to cover than rounds anyway.
Try googling it to see if You-tube has a tutorial. I know with squares you tent out and smooth the corners first and then proceed to the sides. For me it's so much easier to watch a tutorial video than to read somebody's instructions