Nucleon = protons or neutrons.
Binding energy (BE) is how much energy it takes to split the nucleus.
(Explanation will be a bit rough since I'm a little tired..)
A bunch of protons and neutrons are by themselves. In order to "glue" them together to make a nucleus you need to add/invest in some energy to overcome the repulsive force of the protons. Protons (all positive charges) don't like to be near each other so you need to put in some energy to force them to. The strong nuclear force glues the nucleus together. The neutrons also help the protons play nicely together also.
Once you finish your investment, you get a net release of energy because the nucleus is more stable.
The big takeaway is that the mass of the individual nucleons > mass of the nucleus. This mass defect (difference in mass between the 2) gets plug in to E=mc^2 and tells you how much net energy you release.
Little mass difference still gives release lots of energy due to c^2 constant.
The binding chart tells you how stable each nuclei is. The higher the BE the more stable it is. (the chart reminds me of a carrying capacity curve..It very steep slope initially, hits it max and then slopes downward very gently.)
In the sun, fusion occurs where smaller nuclei are combined to make bigger ones and energy is release. The largest energy release is the fusion of hydrogen. This is what occurs in our sun and is how the sun release energy.
In fission, big nuclei are split apart and energy is also release. This is what occurs in atomic bombs.
Both of these processes occur and want to go toward iron because iron has the most stable nucleus.
Anything smaller than iron combines through fusion. Anything larger than iron splits via fission.
Hope that helps.
