This might sound dumb

When is day 1 of ovulation? Is it the first day that <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">eve</a> shows? Or is it the first day of highest chance of pregnancy? I’m honestly really confused. We just started TTC about 2 weeks ago and I really don’t know how to go about it? Does DPO start the first days after ovulation or the day after the last day of ovulation. TIA