Ovulation

Ok, I'm new to tracking things, and I'm a little confused... I thought that you got a positive ovulation test the day you ovulate, but then I read that it is actually within 24 hours of the surge? So, Glow predicts that I will ovulate tomorrow, but if that were the case, I should have had my LH surge today, right? Ugh, why is this whole process confusing?!