A shell is like the floor of an apartment building while the subshell is like little raised platforms on that floor. All the subshells are part of the same shell, but they each have slightly different energy levels. The 2s shell is like the flat ground of the second floor while the 1s shell is like the flat ground on the first floor.
As for the second question, Argon IS a noble gas because it's outer shells ARE filled completely.
I think you might have said Argon when you meant Nitrogen.