This is basically unsweetened, highly concentrated milk. It's normally sold ready-made in cans at most supermarkets, but in case it is not available to you, you can make evaporated milk by reducing or evaporating away much of the water in milk. Don't boil it, because it will scorch and stick like mad to your pan. Simmer it gently on low heat until it is reduced by more than half. Use a non-stick pan if you can. Commercially produced evaporated milk has had 60% of its water removed. So simmer your milk until it is less than half of the original amount. Best results are with whole milk.
Condensed Sweet Milk
This is highly concentrated, thick milk that is sweetened. It is used mostly in desserts and to make toffee or as a sweet topping. It also comes in cans and is easily available in supermarkets, but in case you need to make it at home, here is how to do it. Take 1 cup of Evaporated milk (explained above) and add 1 and a quarter cups sugar to it. Simmer on low heat until the sugar dissolves and the milk thickens slightly more. Turn off the heat and use.