Earth spins on its axis in an anti-clockwise direction when viewed from above the North Pole. This makes the Sun appear to rise in the East and set in the West. At any time, one side of the Earth is lit by sunlight and the other is in shadow.
It takes 24 hours for Earth to make one complete rotation about its axis. This period is known as a Day and is split into Daytime and Nighttime. When a point on the surface of Earth is facing the Sun it is in Daytime, when a point is facing away from the Sun and in shadow it is in Nighttime.
Daytime and Nighttime always add up to 24 hours, but the lengths of Daytime and Nighttime vary depending upon the angle the Earth's axis is tilted.
Earth's axis is tilted between -24.5° and 24.5°. As Earth revolves around the Sun, the angle Earth's axis makes to the Sun changes, though the axis always points to the same point in the heavens. This means that during the Summer the North Pole is facing the Sun and in Winter the South Pole is facing the Sun. During Summer this makes daytime in the Northern Hemisphere longer than nighttime, and the nighttime longer than daytime during Winter. The opposite is true in the Southern Hemisphere. There are two special days called Equinoxes, when Earth's axis isn't tilted towards the Sun and the daytime is the same length as the nighttime.
Change the angle of tilt in the interactive to see what happens: at one extreme the North Pole will have daylight all day round (the Midnight Sun), whilst at the South Pole it will be dark all day; at the other extreme the South Pole has daylight all day round and the Northpole is dark all day.