At different times of the year we can see different stars in the night sky. The positions of the stars relative to each other in the sky stay the same; because the stars are so far away compared with the distance that the Earth travels in a year, changes in the Earth´s position do not shift our point of view enough to change patterns that the stars make in the sky. What does change is what part of the sky we are looking at. Since you can only see the stars at night, when your side of the planet is facing away from the Sun, you can only see the stars that are in your view if you are looking away from the Sun. As the Earth goes around the Sun, the direction you are looking at night changes so you see different stars.