It’s because the earth isn’t only spinning to give us day and night, it is also travelling around the sun in a big circle. It takes a whole year to go all the way round. For about half the year the bottom part of the earth is leaning away from sun, so it’s colder there. The top half is closer to the sun and warmer.
The closer you live to the middle of the earth, the less the weather changes. But further away, the weather is more changeable and there are different seasons. Do you know the names of the seasons and what the weather is like in each?
Did you know that the earth is slightly tilted? And it spins around an imaginary line drawn through the north and south poles. The line is called on axis.