Help with the term # pass days of ovulation

Jasmin • TTC since 02/15 waiting for our first born!
Wen do I start my count? In DPO? The first day of me Ovulating or my period? i dont understand like ex. Someone says im 10 days past ovulation! .. k since wen did they count? Lol I hope u understand lol! Thank you guys for the help!