When playing League of Legends or any other videogame for that matter that has a ranking system, players generally seek to improve their knowledge, strategy, gameplay, etc.
This app is designed to present your post-game statistics in such a way that you can visually see your improvements game-by-game and can compare stats to others.
The intended effect is to gradually help players improve.
All you need to do is put an ign (in game name), and let the app handle the rest.