  The power graph $\mathcal P_G$ of a finite group $G$ is the graph with the
vertex set $G$, where two elements are adjacent if one is a power of the other.
We first show that $\mathcal P_G$ has an transitive orientation, so it is a
perfect graph and its core is a complete graph. Then we use the poset on all
cyclic subgroups (under usual inclusion) to characterise the structure of
$\mathcal P_G$. Finally, the closed formula for the metric dimension of
$\mathcal P_G$ is established. As an application, we compute the metric
dimension of the power graph of a cyclic group.
