The Earth receives light from the Sun. Due to the spherical shape of the Earth, only half of it gets light from the Sun at a time. The portion facing the sun experiences day, while the other half away from the Sun experiences night.

The comparison between axis and orbit is as follow:
Axis The axis of the Earth is an imaginary line which joins North Pole to South Pole and makes an angle of 66 1/2°. with its orbital plane.
Orbit The Earth moves around the sun in a path which is called orbit and it is an elliptical path.

The plane formed by the orbit is known as the orbital plane. The axis of the Earth (an imaginary line) makes an angle of 66 1/2°.  with its orbital plane.
Due to the Earth's spherical shape, only one part of it receives sunlight while other half remains dark.

The North Pole remains inclined towards the sun for six months due to which places beyond the Arctic circle experience continuous daylight for about six months while South Pole remains away from the sun for six months and experiences night for same period. The same condition reverses for the next six months when South Pole inclines towards the sun and experiences day while North Pole experiences night

The seasons are changed on the Earth because of the inclination of the Earth's axis in a fixed direction and due to the change in the position of the Earth around the sun.
On 21st June, the Northern hemisphere is tilted towards the sun. These areas receive more heat because the sun rays fall directly on the tropic of Cancer.
The tropic of Capricorn receives direct sun rays due to tilting of South Pole towards the sun on 22nd December.
The Northern hemisphere experiences autumn season while Southern hemisphere spring season on 23rd September. On 21st March, itIS spring in Northern hemisphere and autumn in Southern hemisphere.