I primarily use it to cook with, or as previously said, keep food warm. I have been known to freeze a "soda / pop can" in foil. It keeps the cold in also.
What is the reason for using aluminium foil to wrap food items?
Umair rehan explained most of it but as an extra fact
Those facts umair rehan gave also apply to some other metal that I can't remember the name of but they don't use the other metal because it is poisonous