You are a little green alien and your mission is to impregnate as many women as possible. To do this you need to be attractive to the ladies. So, go to the gym, study at the university, and you will be more desirable to the earthly women. You also need to sleep and eat to have enough energy, and of course work to buy food and gifts. If you don't have any luck with the girls, you can visit the hotel and get a hooker.