Chop the cabbage
Grate the beet
Squash the mix a bit (with your hand). Put the mix in a bigger bowl or a pan, put a plate over it and put something heavy on the plate.
And leave all like this for 3 days (room temperature). Note that it probably will have more juice in 3 days, so preferable put a larger plate under your bowl.
After 3 days cabbage should be crunchy. Put it in a jar and keep it in the fridge.