how do you know for sure?

Ok so I know a good amount about sex ed but when it comes to ovulation is it when you no longer have the mucus and all that it's done or am I just being stupid about this?? I have gone over many classes on it but for some reason it was never said in a way for me to truly understand so if anyone with a better understanding could help that would be amaizing!!! And thank you for taking the time to read lol