When to bd during your ovulation time

So I've heard that you are supposed to bd right before you ovulate and not during and then I've heard on your higher chance for pregnancy day you bd and bd every other day before and after that. Which one is true? What's the best day to bd? I am not even sure when I am ovulating other than this app, I don't really want to buy ovulation strips, I would rather do it without buying extra things. Thanks!