Answer: Throughout the year, different parts of Earth receive the Sun's most direct rays. So, when the North Pole tilts toward the Sun, it's summer in the Northern Hemisphere. When the South Pole tilts toward the Sun, it's winter in the Northern Hemisphere.
It's impossible for it to be summer and winter in the same hemisphere because the southern and northern hemispheres have their seasons inverted. For example; when it is summer in the US it is winter in Australia.
Hope this helps :)