As the Earth spins on its axis giving us night and day, it also moves around the Sun in an elliptical orbit or elongated circle.
The trip around the sun take 365 1/4 days to complete.
Since the Earth's axis is tilted at 23.5 degrees, the most intense light from the sun will hit different parts of the earth at certain times along trip.
Depending on how much direct sunlight you have will determine which season you are experiencing.
When the Earth's axis points towards the Sun, it is summer for that hemisphere.
Therefore, when the Earth's axis points away from the sun, winter can be expected.