Step 1:
1) add a bit of icing sugar and around 1 tsp/tbsp of cocoa. Step 2:
2)put a few drops of water (not too less and not to much) and mix. Step 3:
3)it should be a bit runny. Step 4:
4) now melt the butter. Step 5:
5) add the melted butter to the icing and keep mixing. (if you stop mixing then it will become hard.) Step 6:
6) spread on top of cake or whatever you are putting it on.