To enter your daily data, click on the + in the upper right corner, or the date in the 'Calendar' or 'History' view. Enter your temperature and choose whether it's a 'Normal temp.' or an 'Excluding temp.' Any additional data, such as your period, sex, LH test result, notes, etc., click save, and you're all set!
In this view, you can also swipe to the left to go back to see your previously entered data. If you have entered any data and swipe back, your data will save automatically!
As a new user, you may want to add your previous cycle data. You can read more about this here.