To freeze milk, simply open the milk and pour out a little because milk expands when it freezes. Enjoy your glass of milk and replace the caps tightly and put into the freezer.
It works best if you can put the milk in the freezer standing up to avoid leaks, but once it is frozen you can certainly move it to a horizontal position.
When you're ready to drink it, just put in the fridge for 2-3 day and shake occasionally to break up the ice. It tastes the same, I promise.