As the earth orbits the sun, taking one year to complete one circuit, it appears to us on earth that the sun moves around our sky once against the background of stars. Here's an analogy--If you walk around a campfire (the sun) looking at your friends on the other side (the stars), to you it would look like the campfire moves past your friends. Likewise, from earth, it looks like the sun moves against the background of stars, making one circuit of the sky in one year.