Seasons happen because Earth's axis is tilted at an angle of about 23.4 degrees and different parts of Earth receive more solar energy than others. Earth's orbit around the Sun is elliptical. Seasons are caused by Earth's axial tilt and temperatures and nature's processes are affected. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.