Induced map from sheaves into cohomologies?

Question

Suppose I have an short exact sequence of sheaves: $$0 \to \mathcal{E} \to \mathcal{F} \to \mathcal{G} \to 0$$ My book says that this induces a long exact sequence of cohomologies (by snake lemma): $$0 \to H^0(X,\mathcal{E)} \to H^0(X,\mathcal{F}) \to H^0(X,\mathcal{G}) \to H^1(X,\mathcal{E}) \to \cdots$$ How exactly does one get this?