Science confusion

The Earth's axis of rotation is not perfectly perpendicular to the plane of it's motion around the sun. It's tilted at an angle. During the Earth's motion around the sun, different parts of the Earth are struck more directly by its rays. The part of the Earth in winter during some part of the year is the part that the sunlight hits at a steeper angle so that the sunlight has to travel through more atmosphere to reach the ground.

Like this:

You can try to Google "Earth seasons", too, if you like.