Touch the plus sign in the upper right corner of the Home screen. Enter the first day of your period and the duration (number of days bleeding) or the last day. Save and repeat to enter additional periods.
Tap "Today" tab to enter notes and periods for today. On the Notes screen, select "first day of period". Choose to use your average duration or mark your period day by day. When marking day by day, select "extend period" from the notes screen to record another period day. Trim a period by double clicking on an existing period day and selecting "last day of period".
On the Calendar screen, double tap any day to enter periods and notes for that day.