A family around one star
The Solar System formed about 4.6 billion years ago from a collapsing cloud of gas and dust. Most of the material fell into the centre to form the Sun; the rest flattened into a spinning disk where the planets grew. That is why the planets orbit in nearly the same plane and in the same direction.
Rocky and giant planets
Close to the young Sun it was too hot for ices to survive, so the inner planets — Mercury, Venus, Earth and Mars — formed from rock and metal. Beyond the 'frost line', ices were plentiful and planets grew large enough to capture hydrogen and helium gas: the gas giants Jupiter and Saturn, and the ice giants Uranus and Neptune.
Small worlds
The asteroid belt between Mars and Jupiter contains rocky leftovers. Beyond Neptune lies the Kuiper Belt, home to Pluto and other icy dwarf planets. Comets are icy bodies that, when they approach the Sun, grow glowing comae and tails. Far beyond, the hypothesised Oort Cloud may hold trillions of comets.
Scale
Distances inside the Solar System are measured in astronomical units (AU), the mean Earth–Sun distance of about 150 million km. Neptune orbits at about 30 AU; light from the Sun takes over four hours to reach it.