Exploring our solar system
The orbits of the planets in the Solar System are almost circular - with the Sun near the centre. Many diagrams (including these here) show the orbits very squashed from top to bottom. This is to give a sense of perspective, or to fit the diagram into a page in a book.
Circular motion requires a centripetal force. Without it, the object will fly off in a straight line. The Sun's gravity keeps the planets, dwarf planets, comets and asteroids in orbit. The gravity of a planet keeps its satellites in orbit.