The outlet behind the fridge is 120V, so that's what the regular 120V plug goes into.
You also need a 12V
supply, for the electronics of the board. As Don pointed out, there isn't one of those in the refer's back cabinet; you need to find a source for that.
But I think it might be time to involve an expert, to get you by this part safely. Electrical work can be tricky, if you aren't experienced.
It's important that you are safe. Saving money is important, but being safe is more important, wouldn't you agree?