In an energy diagram, the height is the amount of energy for the corresponding species.
The left part of the diagram are the reactants and the right part are the products. The pick is the activated complex.
To see if the reaction is exothermic or endothermic, we can focus on the reactants and products only. Notice that the rectants (left) are lower than the products (right), which means that the species in the products have more energy than the species on the reactants. Thsi energy is not created, it was absorbed by the reaction.
Since the reaction absorbs energy to increase the stored energy in the species, the reaction is endothermic.
