Once you have done the marzipan layer, the fondant layer can be applied in exactly the same way.
Knead some fondant until smooth, and roll it out. Apply a light coat of water to the marzipan to give the fondant something to stick to. Press the icing onto the cake and around the edges, then rub over the smoother or the flat of your hand to smooth it out. Trim off the excess icing with a sharp knife, and smooth out any remaining bumps.