To set up a period and view your ovulation/fertile days, do the following.
1) First, open the period tracker and go to settings by clicking on the big (+) button while on the tracker. Here you need to set your default cycle length (This is a one-time step).
2) Whenever you get your period, log the first day of the period by selecting the date and then tapping on the "First day of period" toggle
3) You can log your bleeding days (the days that you are bleeding once your period starts) by toggling the bleeding toggle and selecting the correct days.
4) Open Ovulation Tracker from the home page and your ovulation dates would be marked in green.
I hope this helps.
Please let us know if you have more questions.