why do we use different types of milk on making a milkshake?

Question

and why would anyone use a different type of cream when making something. there's like single cream and double cream. what are they and what's the difference

Answer 1

Different types of milk (skim, 1%, 2%, and whole milk) will give you different flavor. The higher the fat content, the richer and creamier it will taste in your milkshake. The highest fat content of milk is whole milk.
As for creams - there is half and half (which is half milk and half cream) which is often used for coffee, and then there is heavy cream - which is full creamy and VERY fattening. Something like 8g of fat per tablespoon roughly. Heavy cream is often used in cooking and will thicken to make sauces or can be whipped up to make toppings and whipped cream.

Answer 2

They have different fat content, which affects the texture of whatever it is you're using it for. Sometimes you need something with a higher fat content to hold the other ingredients together (like how some milkshakes are thicker than others).