When the Northern Hemisphere is tilted towards the Sun, it receives more direct sunlight and the days are longer. This is why summer occurs in the Northern Hemisphere during the months of June, July, and August.
At the same time, the Southern Hemisphere is tilted away from the Sun, so it receives less direct sunlight and the days are shorter. This is why winter occurs in the Southern Hemisphere during the months of June, July, and August.
The tilt of the Earth's axis also explains why the seasons change throughout the year. As the Earth orbits the Sun, the Northern and Southern Hemispheres take turns being tilted towards the Sun, which results in the different seasons.