From Spring to Summer to Autumn to Winter.

They spin, like on a roulette wheel

From Winter, to Spring, to Summer, to Fall and back to Winter again!

Ever since the Earth got knocked off it's rocker, the sun can't reach all parts at the same time. When Earth leans toward the sun, it shines on the upper part, making it warmer. When Earth rolls around the other way, the sun shines on the lower part, making it warmer. So, half and half, one side gets Spring/Summer, while the other half gets Fall/Winter. The real reason is Ra! All Hail the Sun God; He really is a fun God; Ra! Ra! Ra!

The Earth spins around an imaginary axis that goes from the North Pole, down through the centre of the Earth to the South Pole (1 spin = 1 day). The Earth also orbits around the sun on a nearly circular track (1 orbit = 1 year). The imaginary spin axis line is NOT at right angles to the orbit path. It's tilted by 20-odd degrees, so the Earth goes around the sun with some parts getting the sun more "square-on" than at other times. (The seasons) When the bottom of the Earth faces the sun more square on (Southern hemisphere summer) the top half is tilted away so the sun comes in at a more oblique angle and gets warmed less (Northern hemisphere winter.) The easiest way of seeing this by yourself is to google "how do seasons change" for some animations. The easiest way of seeing this with someone else is to expose a bulb (the sun) and to borrow a globe that sits on its tilted axis and get them to move the globe around the bulb. The tricky bit is to keep the angle of the tilt the same with respect to the room. i.e. pick one wall and aim the tilt at right angles to the wall. Keep the tilt at right angles to the same wall all the way around the sun. The imaginary spin axis line does not change direction as the Earth goes around the sun when seen by an observer looking from above. Much easier to watch an animation than to describe!