Katarina can be a very broken champ to play if you can play her right. I do not like playing a Kat in norms due to the fact that I dominate every game and it does not seem fair to the other team or my team from kill stealing and hogging the glory. She is an easy champion to get an S-, S, or S+ on but she can be a pretty hard champ to START to learn the game on. Start safe and get progressively more aggressive when the game continues. The more focus on other players on your team and not you, the better. Build accordingly to what you are playing against (AD = Armor and magic Pen) (AP = Magic Resist, and magic pen). Most importantly, have fun. :)