When you first open the app, you'll be greeted by the home page. At the top, you'll see a button that says: “Start tracking your macros now!”
You can also tap the tracker menu item in the bottom menu:
Once you tap it, you'll be asked a few questions about your current weight, gender, body fat percentage, daily activity levels and goals. The app will then provide you with calculations that are optimal for hitting your goals at an effective yet safe speed.