I am reading about kronecker symbol, and I have read that this simple has no connection to quadratic residues. This make me very confused since quadratic reciprocity very related to quadratic residues since it depends on the definition of Quadratic residues. Whereas the Kronecker symbol has a quadratic reciprocity law. But then what does the quadratic reciprocity for kronecker symbol say about the solvability of the congruence $x^2 \equiv m \mod n$ for positive integers $m$ and $n$ ( not necessarily odd when applying kronecker symbols)? and what is the importance of this symbol?