Seasons
Earths seasons are caused by the Earths rotation around the sun. While the Earth is orbiting the Sun, then the light distances change. The Earth has seasons because it has a tilted axis as it revolves around the sun.
As you can see in the picture, the Earths tilt decides the seasons. For half the year, the suns tilt is towards the sun, and for the other half it is away from the sun. There is a 23.5 degree tilt in spring and fall. When the Earth is tilted towards the Sun, it is Winter whereas when its tilted away from the Sun, then it is summer.