You will need:
Butter depending on how much icing you want to make and for what.
A little bit of milk.
Food coloring or flavor- optional.
The first step is to put your room temparature butter in a hand mixer and beat it for 5-6 minutes. The reason is that the butter will become light and turn white instead of it staying yellow. It will also large a bit in size.
Slowly add the icing sugar and make sure there are no lumps. Add slowly little at a time because you will stop at a certain point for the consistency you want.
Add milk if you feel it starts to thicken up too uch and add flavor and food coloring. Blend well- Don't overblend.
INFO / TIPS
For the food coloring its best that you add it with the milk because some food coloring tends up to create lumps so make sure you are either using good quality or add a bit of milk.