In a lockable water bottle, you can use a plastic jug, glass bottle, old soft drink bottle anything you like.
Being scientific, not, I chucked in a load of grounds.
This will take some working out for how strong you would like your coffee.
Fill to the top with water.
Give it a shoogle to mix the coffee and place in the fridge.
One thing not to do is use hot coffee and add ice - coffee is high in chlorogenic acid, which, as the coffee cools, forms quinic acid which makes the coffee bitter. Plus it waters down your coffee, and you don't want that.
After about 12 hours, remove from fridge.
I used a tea strainer to remove the grounds. Then added some milk to taste. No sugar was needed as it wasn't bitter at all.