@Majem I hate Attacks of Opportunity, to be honest. Worst system Paizo created, not because they are a bad system but because they were poorly thought of. To be honest, they probably won't be used in forum play like this because we aren't using a tabletop map like we'd use in an in-person game or by playing via roll20.
But I'll still try to explain as well as I can.
For instance, let's say we were playing this on a tabletop and the last turn happened where you went down. Getting up from prone, which is what you were while down, provokes an attack of opportunity from any enemy within one square of you on a tabletop map. So in this, the bad guy would have been able to attack you as you got up, before your attack.
If you decided to move on the map to pass a bad guy to attack the guy behind him, provokes. If you had a healing potion standing in front of that guy, drinking it provokes. If Orina was standing next to a bad guy with a melee weapon and shot an arrow, that provokes.
Really, while the system isn't all bad, there are a lot of things that provoke and end up confusing players, and especially new players and GMs.
If you wish to try and use Attacks of Opportunity, I'll let you because some have some obvious benefit... But I really don't think it will be easy in a forum setting, nor do I really enjoy them.