TTC buddies!

Ta
I'm confused by the ovulation window lol. So the way it tells you on here is it has the green highlighted days and then it tells you the percent chance of getting pregnant. My questions are: 
1: do you have sex BEFORE the first green highlighted day comes? If so, how many days before? Or just anytime during those green days? 
2: when it says "33% chance of pregnancy" does that mean to have sex on that day or to have sex a day or two days before that day comes? 
New at TTC so trying to get it right lol, thanks ladies