Describe all semidirect products of $C_n$ by $C_m$ (ie $C_n \rtimes C_m$) where $m,n \in \mathbb{N_+}$
Note: For the first attempt one needs to find all homomorphisms from $C_m \to U(n)$, but the situation differs a lot for different pairs of $n ,m$, is there a better way to find all structures of $C_n \rtimes C_m$?
Wikipedia provided a general presentation of this product which I do not know how it was worked out.