Your chart starts on the first day of your period. This is the first day that you have red flow (not spotting). This is cycle day one. When you enter menstrual flow data, a new chart will be started for you.
If you start charting mid-cycle, make sure your chart still reflects cycle day one as the first day of your period so that your cycle statistics will not be skewed. In this case, you can go back and enter your period information on the date your period started and cycle day one will be reflected for that day.
If your period arrives in the night or late in the evening, you can record it for the following day.
Record, "light", "medium", or "heavy" to relatively describe your menstrual flow from day to day.