Remove the cooled cake layers from the pans. Make sure that they are completely cooled to room temperature.
**not required but highly recommended** Cover the layers completely in plastic wrap and place them in the freezer for 2-3 hours. This makes cake frosting much easier.
Pick the plate that you will be setting your cake on and place a small amount of frosting in the center of the plate (this will act as "glue" for the cake so that it doesn't slide around the plate).
Place your first cake layer over the frosting dollop and spread a thick layer of frosting evenly over the cake. Make sure that the frosting is flowing past the edge of the cake (this makes it easier to frost the edges once fully assembled).
Place the second layer on top of the frosting layer and repeat the step above.
Place the final cake layer on top and add a final thick layer of frosting that is overflowing over the edge.
Use a butter knife, offset spatula or piping bag to add a thick layer of frosting around the sides of the cake. It's okay if the frosting still looks messy at this point!
Use the flat end of an offset spatula, a rubber spatula or (ideally) a cake decorating icing smoother or flat edge bench scraper to smooth the frosting around the side of the cake.
If you would like to add additional decoration on top of the cake, place the remaining frosting in a piping bag with a decorative tip and pipe around the edges. I have included links to my favorite cake decorating tools in the post above!