If you take a look in your player profile, you'll see that you have something called mastery trees. These are pretty much equivalent to the talent trees found in World of Warcraft and many other popular games, and allow you to "spec" you character for offense, defense, or utility. You'll receive one mastery point for every level you gain on your account (Account levels are NOT character levels, so be sure not to get those mixed up. Account levels are permanent and go to level 30, your character will have to start at level 1 each game and can go to 18).
Runes are another way to customize your character, and can only be earned by playing games, and basically allow you trick out stats that you'd like to see on your characters from game to game - Extra critical strike chance, mana regeneration, health regeneration, that kind of thing.