Mix ur butter until soft then add ur icing sugar gradually while mixing until u add all, then mix until fluffy. Add your milk and vanilla extract and mix for a min.

Then get ur cake and place on a cake board, then place on a cake turntable. Use your spatula and put the frosting on your cake, then use ur palette knife to spread it while turning ur table. After that, use the cake scrapper to smoothen it.

Use a piping bag and nozzle and create any design of your choice