On Espresso mode: Enter the amount of coffee for your shot, then you have two options, if you know how many coffee you want out enter that value and the all will tell you the ratio for that setting, and if you know the ratio you want, then set that one in the app and it will tell you the coffee you'll be getting out. so you'll know when to stop the machine. There are also five predefined ratios for common recipes.

On Coffee Mode. if you know a recipe you can enter its value in the app, or enter the coffee in and use one of the predefined options. this will tell you the amount of water you'll need to pour for that given recipe. Using the lock button will set the ratio for the recipe, editing the coffee in will change the water needed, and editing the water needed will change the coffee in value.
If you're more confortable using ratios instead of grams per liter, you can switch to that by taping on the grams per liter value.