Having two prime numbers $p$, $q$ and a relation $N=pq$.

**How could I find the order of group $\mathbb{Z}_{N^2}^{*}$?**

I know that $ord(\mathbb{Z}_{N^2})=N^2$ and that $\mathbb{Z}_{N^2}^{*}$ is a subgroup of $\mathbb{Z}_{N^2}$.

Also I know that the order of the group is divided by the order of its subgroups, so $ord(\mathbb{Z}_{N^2}^{*})|ord(\mathbb{Z}_{N^2})$.

So, the possible orders could be either $N^2, N, p , q, 1$, but thats where I get stuck: I don't know how to determine which one would be the right order?

Could you give me any hints how to solve this problem?

Edit:

"What does the ∗ mean in this case?"

$\mathbb{Z}_{n}^{*}=\{a \in \mathbb{Z}_{n} : gcd(a, n) = 1 \}$