The binding energy ber nucleon curve can help you see which processes release energy. For example if two Hydrogen atoms fuse to make Helium, since the end product (Helium) is higher up, energy is released. The same with fission of e.g. Uranium.
Elements that have high B.E. per nucleon are more stable, you might notice that Helium is up on a little spike, higher than the surrounding elements, Helium is stable.
The highest are in the region around iron, these elements are stable, no energy would be released if it were possible to do fusion of them - and more energy is needed than for other elements to split them up.
In practice fusion can only occur with the few lightest elements and fission with a few of the heaviest.
Here is a diagram of B.E. per nucleon