If you want to battle, you need a commander. Every commander has three specialty that determine which talent trees can be leveled. Every commanders has four skills, which are unlocked according to the commanders star level. Epic and Legendary commanders have a 5th mastery skill that enhances one of their first 4 skills; it is unlocked by getting all four skills to level 5. Star levels can be unlocked by sacrificing sculptures, which can be specific for that commanders or a general sculpture.