To attach the gold leaf to the cake, dampen a fondant-covered cake just enough that it's sticky, then carefully press the gold leaf sheet onto the cake. Rub the whole surface gently, then remove the backing paper carefully and the gold will adhere to the tier. If it doesn't stick, you can put it back down and press it in the place it didn't stick and it will probably stay in place. You can use a very soft paintbrush to pat the gold leaf down into place if it sticks up from the surface. If there are holes in it you can go back and place some more gold leaf over the hole to cover it up.
Kara Buntin owns A Cake To Remember LLC, online cake supplies at www.acaketoremember.com and www.acaketoremember.etsy.com