The Oort Cloud is a sphere of icy rocks surrounding the entire Solar System it is at a distance of 2 light years away, meaning it takes light, travelling at 300,000 kilometers every second, 2 years to get to us from here. The Kuiper Belt is a disk of these icy objects which sits in line with with orbit of the planets in our Solar System, from Neptune further out. Pluto and many of the other dwarf planets in our Solar System are found in the Kuiper belt.
There are at least 100,000 icy and rocky objects in the Kuiper Belt, in fact some of the moons of Saturn and Neptune are thought to have originated there.
It's thought that the edge of the Oort Cloud marks the edge of our Solar System, though astronomers have yet to actually observe this part of the Solar System. We think that most of the comets in our Solar System come from here.