When you write the reaction, it is shown below:
CH₃OH + CH₃COO⁻ → CH₃COOH + CH₃O⁻
Since no figure is given showing the direction of the curves, I can't be really sure what you are referring to. However, I would guess that the first arrow is from the H atom of methyl alcohol transferring to the acetate ion. As a result, the methyl alcohol turns into an anion called methoxide.
