The reason so many objects orbit the Sun in nearly the same plane (called the ecliptic) and in the same direction is that they all formed from this same disk.
While the planets were forming, there was not much peace in our solar system. Clumps of matter of all sizes often collided, and either stuck together or side-swiped each other, knocking off pieces and sending each other spinning. Sometimes the gravity of big objects would capture smaller ones in orbit. This could be one way the planets acquired their moons.
