On the first step, the epoxy-oxygen is proronated and acquires positive charge.

On the rate-limiting second step, the positively charged oxygen pulls an electron pair from its bond with carbon, breaking the bond, and forming a carbocation.

On the third step, the carbocation pulls an electron pair from oxygen of methanol, forming a C-O bond and shifting the positive charge to oxygen.

On the forth step, the positively charged oxygen pulls an electron pair from its bond with H, releazing a proton to the solvent.