Before placing fondant on a cake make sure that you have iced the cake with butter cream icing so that the icing works as a glue that will hold the fondant in place. Once you have iced the cake go on to these next steps.
1. Make sure you have a fondant mat, or are using a clean counter top. Start buy rolling out the fondant with a roller if it gets sticky you can use Crisco vegetable shortening or confectioners' sugar to keep it from sticking to the roller or mat. Roll out the fondant to the size of your cake.
2. Gently lift the mat on which the fondant is on if you are not using a mat you can always just pick up the fondant very carefully. Gently place fondant on cake. If you are using the mat peel off mat very slowly once the fondant is touching the cake.
3. You can use a fondant smother to smooth out the fondant on the cake or you can use your hands (as long as they are greased with Crisco shortening). Begin by smoothing the middle of the cake and then the sides. If you get an air bubble you can pop it with a pin and smooth again.
4. Finally trim off the excess fondant using a sharp knife.