The polar regions are called the "lands of the midnight sun" because in the summer, the sun never sets. Why?

The Earth is tilted in its axis - an imaginary line through the planet between the north and south poles around which it rotates. The tilt always points the same way in space.

The area around the equator is consistently close to the sun, but the areas around the poles are not.

As the Earth orbits around the Sun, that tilt makes the North Pole face towards the sun in summer (keeping it in sunlight even as the Earth spins) and away from it in winter (keeping it dark). This means that the Pole gets continuous sunlight (yes, even at midnight) during the summer, but doesn't get any sunlight at all during the winter.

The northern and southern hemispheres experience opposite seasons as the Earth moves around the sun. While the North Pole is in constant darkness (winter), the South Pole is in constant sunlight (summer). For example, in the Northern Hemisphere, Christmas is in the winter - in the Southern Hemisphere (like Australia) Christmas is in the summer.