And the half reaction is simply a way for us to visualize more clearly the transfer of electrons from one atom to another. Because notice in this net reaction, there was no transfer of electrons. We couldn't visualize the transfer electrons. But in these half reactions, we have the plus two E and plus two e.
So this is simply a better way for us to see the movement of electrons. Now, to go back to our net reaction net reduce reaction. What we simply do is we add up the two half reactions.