Okay kiddo, so milk comes from cows, right? Evaporated milk is still milk, but it's been changed a little bit.
When milk gets really hot, some of the water in the milk turns into steam and goes away. That's what happens when you boil water too!
So, they take milk and they heat it up a lot. That makes some of the water in the milk turn into steam and disappear, which makes the milk thicker.
But, they don't heat it up so much that all the water disappears. They're just taking some of the water out. Now it's called "evaporated milk".
It might sound weird, but we use evaporated milk to make all sorts of yummy foods like pudding, pie, or sauce. It can also be added to coffee or tea to make it taste creamy.
See, it's still milk, just less water in it. That's all there is to it!