A round cake is by far the easiest shaped cake to cover with sugarpaste. Your cake should be filled and coated with buttercream. The buttercream will act as a glue to stick the sugarpaste to the cake. You could use jam if you prefer. If you’re worried about the buttercream hardening and losing its stickability (is there such a word?) before you’re ready with the sugarpaste, lay a sheet of cling film over the buttercreamed cake and remove it just before you cover it.
Dust your work surface with icing sugar (confectioner’s sugar) and knead your sugarpaste until it’s soft and pliable. You can also soften it in the microwave by blasting it in 20 second increments. Make sure you don’t over do it though as hot sugar can burn. Then roll the sugarpaste out on your worksurface. Don’t roll the paste too thin. It should be about 5mm ( 1/4 inch) thick. Lift and place the sugarpaste over the cake.
Using your hands, gently smooth the sugarpaste over the top and the sides of the cake. Then trim away the excess icing from around the base of the cake using a small sharp non serrated knife.
If you have a cake smoother run it over the cake to iron out any lumps and bumps. Cake smoothers are bits of plastic with handles at the back which you hold a bit like an iron. These are how the professionals get their cakes looking so smooth. If you’re going to start cake decorating I would definitely suggest you buy a pair.