Here's a little more detail:

* Not a perfect circle: Earth's orbit is not a perfect circle, but rather an ellipse. This means that Earth is sometimes slightly closer to the Sun and sometimes slightly farther away.

* Gravity is the key: Earth stays in its orbit due to the force of gravity between the Earth and the Sun. This force keeps Earth from flying off into space.

* One year: It takes approximately 365.25 days for Earth to complete one full orbit around the Sun. This is why we have a year.