Okay so, technically, if you have been paying attention, this question has already been answered. But, it is very important so in case you skipped over when it was addressed, you will need to boil the milk before you place it inside of your container or jar. The operating instructions you receive should inform you of how to do so.
The main reason you want to do this, in the first place, is the current milk you are using could contain bacteria that will prove detrimental to your end result. Scalding the milk can then kill these bacteria to ensure it makes no impact.