There are two different ways to add preparations in a recipe. First you need to navigate to the recipe's page. To learn how to make a new recipe, check out this article (How can I add a new recipe).
The first is for components that are already included in a recipe. To do so, select the "Add Preparation" drop-down next to the ingredient that you want to add a preparation to. Type in the preparation you want in the search bar. You can then select a preparation that you have already created, or make a new one. After a preparation is added, you can connect more by clicking "+"
The second way to add preparations takes place as you add components to the recipe. First, press the "+" next to "Components" and type in the ingredient you want to add. Once you have selected the ingredient, you will be directed to an edit screen where you can add preparations and units to the ingredient.