Let $f:(X,\mathcal{O}_X)\to(Y,\mathcal{O}_Y)$, $\mathscr{F}$ an $\mathcal{O}_Y$-module. How is $f^{-1}\mathscr{F}$ an $f^{-1}\mathcal{O}_Y$ module?

Question

Let $f:(X,\mathcal{O}_X)\to(Y,\mathcal{O}_Y)$ be a map of ringed spaces, and let $\mathscr{F}$ be an $\mathcal{O}_Y$-module, then we can easily define $f^{-1}\mathscr{F}$ as a sheaf of Abelian groups. But how do we define the morphism $$f^{-1}\mathcal{O}_Y\times f^{-1}\mathscr{F}\to f^{-1}\mathscr{F}$$ so as to make $f^{-1}\mathscr{F}$ into an $f^{-1}\mathcal{O}_Y$-module?