All machines have switches on them!
For example, when you have the Cheese Machine, it is normally set to produce Cheese from Milk (the Milk of the Cow). When you click the switch, it gives you the options to produce Cheese from Goat Milk and Buffalo Milk as well.
About choosing the ingredients
If the background of the ingredient is white, this means you have a supply of this ingredient in your barn. If the background is grey, it means that you don't have this ingredient at the moment. You have to grow or produce it first, before you can use this in the machine.
For example, if you click the switch on the Cheese Machine, and the background of the Goat Milk is grey, you can't make Goat Cheese at the moment. You first have to produce some Goat Milk.