How to prove : $6\mathbb Z /24\mathbb Z $ is an ideal in $\mathbb Z /24\mathbb Z $ , what are elements of $6\mathbb Z /24\mathbb Z $

Question

Prove : $6\mathbb Z/24\mathbb Z$ is an ideal in $\mathbb Z/24\mathbb Z$. Is this ideal maximal? Is $\mathbb Z $ /24$\mathbb Z $ an integral domain?
I don't know what are elements of $6\mathbb Z/24\mathbb Z$, that's why I don't know how to start with this proof. What I know: $\mathbb Z/24\mathbb Z$ contains the 24 residue classes. So: $\mathbb Z /24\mathbb Z =\{0,1,...,23\}$.