Let $F, G:\mathcal{C}\rightrightarrows\mathcal{E}$ with $\mathcal{C}$ small and $\mathcal{E}$ locally small. Prove that the end over $\mathcal{C}$ of the bifunctor $\mathcal{E}(F-,G-):\mathcal{C}^{op}\times\mathcal{C}\to Set$ is the set of natural transformations from $F$ to $G$.
How would I proceed about proving this?