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