What are quantum numbers used to describe?
Quantum numbers are used to describe an atom's electron distributions. Particularly, they represent acceptable solutions to Schrodinger's wave equations for the Hydrogen atom (more here: http://en.wikipedia.org/wiki/Schr%C3%B6dinger_equation )
The quantum number that indicates the orbital is
and so on.
Think of quantum numbers as forming a map to a certain electron's location, each electron having a distinct set of quantum numbers to describe its position.