The tilt of the Earth's AXIS is the most important reason why seasons occur. We have hot summers and cold winters because of the tilt of the Earth's axis. The tilt of the Earth means the Earth will lean towards the Sun (Summer) or lean away from the Sun (Winter) 6 months later.
We have different seasons because of the earth’s constant movement around the sun. The closer a place on earth is to the sun, the warmer it will be. The farther away it is, the colder it will be.