The earth's axis of rotation is tilted. because of this, the amount of sunlight an area on the planet receives each day varies
depending on the time of year. these variations result in four distinct seasons.
the diagram below shows the earth at one particular point in its yearly revolution around the sun.
image courtesy of nasa
when the earth is in the position shown above, the northern hemisphere experiences the start of
hemisphere is tilted
the sun
because that

The Northern Hemisphere experiences the start of summer

Explanation:

Due to this tilt in Earth's axis of rotation, some regions receive different amounts of sunlight according to the seasons of the year. These variations are more evident near the poles and softer or imperceptible near the equator. This explains the fact that while in the northern hemisphere it is summer and there are high temperatures (because the Sunlight incides more perpendicularly in this area during this season), in the southern hemisphere it is winter and very low temperatures are recorded, and vice versa.  

In this sense, according to the image the Earth is at the point of its orbit in which, due to the inclination of its axis, the North Pole is closer to the Sun.  

In other words, the northern hemisphere is tilted toward the Sun, and this astronomical phenomenon brings the summer season for the Northern Hemisphere.