Ovulation

Okay, this is something that’s super confusing to me lately. When people are talking about ovulation, what does that mean? Plus people saying a window where the egg drops is only 12-24 hours and it dies. When does the happen? Then you get your period? I’m just confused. Like if I were to have unprotected sex like idk let’s say 8 or 9 days before my period was supposed to come, then I get my period? Is there a chance that a pregnancy could occur? Even though according to my app it’s not a fertile day and you get bleeding and cramps on the day your supposed to? I’m just confused about a lot... anyone able to help?