The earth also rotates once a day on its axis around the north and south poles. The reason why summer is hot and winter is cold has to do with the earth's orbit and rotation.
The axis of the earth's rotation is slightly tilted in relation to the axis of the earth's revolution around the sun. This tilt causes the Earth to receive more sunlight at certain times of the year and less at other times of the year.
Summer is the time of year when we receive plenty of sunlight and heat. On the other hand, winter is the time of year when we receive little light and heat. Spring and fall are in between summer and winter.
Thus, the seasonal changes, such as hot summers and cold winters, are caused by the earth's orbital motion around the sun.

The earth's axis of rotation is tilted by 23 degrees 27 minutes (about 23.5 degrees) relative to its orbital axis.