Most all orbiting objects move in an elliptical orbit. First, let me explain what an ellipse is. Maybe a picture would be better:
Let us say that you draw a vertical line and a horizontal line. Now, place three pins along the horizontal line, one at the center and the other two equal distances from the center on the horizontal line. If you attach a string that is longer than the distance between the two pins to one pin (F1 in the above view) and the other end of the string to the other pin (F2), you can then use a pencil to draw an ellipse as shown above. Now, what happens if you move the two focal points out or in? Yep the ellipse changes shape. Now, if you move both pins into the center where the lines cross, you will get a circle. A circle is an ellipse with a common focal point.
The planets' orbits are basically an ellipse but they are more like circles with the sun offset to one side. Anyway, so what causes the planets to orbit in this offset circle or ellipse? Any object coming into the gravity field of star, or black hole, or any object larger than they are and gets caught in that objects gravity will be slung into an elliptical orbit. The speed of the smaller object is highest when it is closest to the larger object and slows down enough as it gets further away to allow the gravity of the larger object to swing it back around. So, most objects start their orbits in an elliptical fashion which determines the way it travels around the main object from then on.
Alright, before I start talking in circles or ellipses, I better quit and say, you have a great day, you hear?