When you first start using Natural Cycles, you will not be able to see your fertility status right away. Instead of red and green days, your data will show in black until you log your first temperature.
That is because your basal body temperature is the main data that the app uses to calculate your fertility. Learn more about the fertility indicators used by Natural Cycles here.
Below is an example of an account of a new user without temperature data: 
Once you receive your thermometer and add your first temperature data, this will unlock your fertility status and you will be able to see if you have a green or red day.
Learn more about how Natural Cycles works here.