There are four major seasons in a year-Winter ,Summer,Fall & Spring.At many places in the world rains (rainy time) are considered to be a separate season.These seasons on the earth happen due to earth's movement around the Sun & its constant spinning around its own axis.
Each season lasts for approximately 3 months,summer is the warmest and winter is the coolest one.The earth's tilt on its axis and the earth's rotation are the two major factors of change in the seasons.Tilt of the earth on its axis is also responsible for opposite seasons on two sides of the equator.
Summer :The part of the Earth that tilts towards the Sun has longer days and weather is warm.
Winter:The part of the Earth which is tilted farthest from the Sun receives very less sunlight.Days are smaller and weather is cold.
Autumn:The earth begins to tilt away from the Sun ,bringing in cooler weather.
Spring:The earth begins to tilt back towards the Sun bringing warmer weather