I don't understand how to read the cycle for each period, help? the cycles for my past periods were all different i.e. 15, 36, 17, 19 days etc

Likely normal: It is common to have menstrual cycles of variable lengths. While it is more common for young women in the first years of menstruation to have longer cycles, variability from 21 to 45 days is considered normal during this period of life. This variability may well mean you are not ovulating, and you certainly cannot predict ovulation with this pattern. If needed, practice reliable contraception.

What are you readin?: To track your cycle you only need to record the first day of your period. The number of days from the start of one period to the start of the next is the length of your cycle. This will naturally vary a little from one month to the next. The normal range is 21 days to 35 days(42 according to some sources). You ovulate approximately 14 days before your period starts. Hope this helps.