When the Northern Hemisphere is tilted towards the Sun, it receives more direct sunlight and experiences summer. At the same time, the Southern Hemisphere is tilted away from the Sun, so it receives less direct sunlight and experiences winter.
Six months later, the Earth's position is reversed. The Northern Hemisphere is now tilted away from the Sun, so it receives less direct sunlight and experiences winter, while the Southern Hemisphere is tilted towards the Sun and experiences summer.
The changing seasons are also affected by the Earth's axial precession. This is a slow, regular wobble in the Earth's axis of rotation. Axial precession causes the Earth's axis to point in different directions over a period of about 26,000 years. As a result, the timing of the seasons gradually shifts over time.
The combination of the Earth's axial tilt and axial precession gives us the seasons we experience on Earth.