The Earth spins around this blue line, which is known as the Rotation Axis of the Earth.
But all the planets orbit around this yellow line, known as the Orbital Axis of the Solar System.
We have seasons because the Earth’s axis is titled compared to the orbital axis of the Solar System.
In summer, the Northern Hemisphere tilts towards the Sun, so that we see more daylight (long days).
In winter, the Northern Hemisphere tilts away from the Sun, so that the days are shorter.
The red line is to show that we see more of the Sun in the Northern hemisphere during the summer, and less in the winter.