Why the Earth spins

Earth spins on its axis as it revolves around the sun.

Newton's first law of motion states that an object remains in the state of motion it's in unless another force acts upon it.

Before there were planets in our solar system, there was a spinning nebulous cloud of dust. The spinning dust collided over time and stuck together, forming larger rocks and, ultimately, planets. The cloud of dust was rotating from the start. The angular momentum the Earth needs keeps the world spinning.