First, you'll need to buy a recipe in Pondington.
In the mill, which is also situated in Pondington, you can bake your recipes. In doing so, the required products are taken from your stock.
As soon as the products are baked, the miller indicates this by jumping up and down in front of his mill. By clicking the mill, the goods are transferred to the drawer on the right-hand side of your shelf. You only see this drawer if you are on your first farm. If you click on the drawer, you see your power-up. You can activate by clicking the power-up.
There are different effects of the power-ups.
Let's take the Italian salad, for instance. If you activate this power-up, the yield of your spinach is augmented by one for 48 hours. In place of 4 spinach, you receive 5 spinach plants when harvesting.
There's also a power-up for points, e.g. tzatziki. After its activation, you'll receive +10 points when havesting tomatoes (73 points instead of 63). This lasts for 48 hours.
Another package are the product power-ups. The fish food and the oven potatoes are part of it. Upon the activation of oven potatoes, you'll receive 240 milk.
Please keep in mind those differences. Every recipe and power-up is only usable one time and has to be bought/baked anew.