The Earth's tilt on its axis with respect to its orbital plane is the cause of the different seasons experienced annually. When the Earth is tilted toward the sun, it causes the summer season in that particular hemisphere. Winter is consequently caused by the Earth titling away from the sun.
Earth has two movements. It spins on its axis, completing a rotation every 24 hours, and it rotates around the sun. It moves in an elliptical pattern around the sun every 365.25 days. During this time period, Earth is in a different position every three months. This is caused by the fact that the Earth is tilted on its axis at an angle of 23.5 degrees.
Summer is the time when Earth is moving the closest to the sun. The tilt of the planet is facing toward the sun, which warms the surface. As the planet moves around the sun, it begins to move away from the star, which is when the season of autumn begins.
As of winter 2014, the Earth is beginning to cool down. During the winter, the Earth is titled away from the sun, causing temperatures to drop to their lowest point of the annual cycle.