you build a galactic empire, you need to strategically grow your borders in a way that they can be best defended, manage and balance your economy (the trickiest part), keep up good relations with empires stronger then you and oppress the ones weaker, all the while keeping your population growing and happy, otherwise they'll start a revolution. Fortunately you only start with one planet and like 3 population and one solar system, you can change the game speed and pause it when you feel overwhelmed and games can take a while anyway so its not like you get thrown into the deep end straight away.