Help!!!!

I have endometriosis and my periods for the most part are regular. Give or take a few days. My thing is because I have endometriosis I’m not really certain when my period begins or ends on the exact date to calculate it. So I’m not really sure when I’m ovulating. When I start taking the ovulation kits so I can try better to pin point what exactly do those mean? Like when you get a smiley face does that mean I should be ovulating within the next two days so I should focus having sex then or what? I’m also going to try pressed this month. My chart says I’m suppose to ovulate New Year’s eve. I’m just trying to figure all this stuff out...