1. Seasons are formed because of revolution of the Earth around the Sun.
2. As Earth is tilted at an angle on its axis, one pole is near to the Sun and that hemisphere experiences summer.
3. The other pole that is far from the Sun, that hemisphere experiences winter.
Note: The Earth revolves around the Sun in an orbit. The Earth rotates on an imaginary line called its axis. The axis passes through two points, top one is called North Pole and bottom one is called South Pole.
Equator is an imaginary line that goes around the Earth and divides into equal parts. The upper half is called Northern Hemisphere and lower half is called Southern Hemisphere.