This video only shows how I cover a square cake (none of the prep work). In order to achieve a good finish you need to cover the cake with ganache first, you need to achieve a perfect finish with the ganache first, as you would if you were covering a cake in butter cream. You then allow it to set overnight. You need to roll your fondant fairly thin (no more than 3-4mm thick).
Once you've done what's shown on the video, you will need to do further smoothing.