Earth does not spin perfectly upright. Its rotation axis is tilted about 23.5 degrees compared to its path around the Sun. That lean stays pointing roughly the same direction in space as Earth orbits. Because of the tilt, different parts of the planet receive more direct sunlight at different times of year. This tilt is the main reason we have seasons, not because Earth moves dramatically closer or farther from the Sun.
📐 TILT
Earth's axis tilt is about 23.5 degrees. That angle is the key driver of seasonal changes around the world.