The four seasons of the year are winter, spring, summer and autumn. Each of these seasons occur depending on the Earth's position in its orbit and the tilt of the planet as it moves through its orbit.
Winter officially begins in the northern hemisphere on December 21st of every year, this is also called the winter solstice. The northern hemisphere is tilted away from the sun at this point in the Earth's orbit around the sun which causes the area to have more hours of darkness than of daylight. The tilt of the planet means that there is less heat gained from the sun during this time. Spring begins during the vernal equinox, which occurs in March for the Northern hemisphere. During this time the planet gets equal hours of day and night, beginning a warming trend as the planet continues its orbit around the sun. The days being to get longer during this time period as well. Summer begins on the summer solstice which is June 21st and also the longest day of the year. The days are longer than the nights at this point and the temperatures go up as the northern hemisphere is tilted towards the sun. Fall, which begins in September on the autumnal equinox, shows a shortening of days and cooling of temperatures as the northern hemisphere begins to tilt away from the sun once more.