Answer:
This belongs in astronomy.
It's a theory of how solar systems have come to be.
Basically, clouds of gas draw together and form an accretion disc (which lies in a plane equal to the planets' axes).
In the center a sun is created from the large amount of particles gathering there.
Elsewhere particles gather and form larger particles, which collide and gain size over time.
After a long, long time a solar system has been created.
All the details are not known, and this was probably the most simplistic explanation of the theory possible, try searching for accretion disc.