points in affine toric variety

Question

I am reading Toric Variety from Cox, little and In proposition 1.3.1, I saw this proposition about which I have one question As you can see, they have written that the map $\gamma: S \rightarrow \mathbb{C}$, induces a surjective $\mathbb{C}$-algebra homomorphism from $\mathbb{C}[S] \rightarrow \mathbb{C}$. I cant figure out what will be the induced map,It will be great if you an give me some idea how the induced map will look like?