So the y axis is the energy, the x axis is the reaction progress, it's the time. So we have the reactants and this is the energy of the reactants. We have the products, this is the energy of the products. Now for the forward reaction going this way, we see that the reactants are at a higher energy level than the products and that means this is an exothermic reaction. So going this way in the forward direction we have an exothermic reaction and energy is released into the surroundings. Now for the reactants to actually transform into the products, we have to input enough energy.