When I know fermentation is done and I've let my fermenter sit for however long I want it to go for, I put it into my keezer. It sits around 40 degrees and I let it sit for 3 days. Some people go longer, some go shorter. It's whatever you feel like doing really. Cold crashing, you really can't screw up unless you get it too cold and freeze your beer. This is just from my own experience though.