Answer:
[Fusion: Nuclei Fuse together and release energy] [Fission: Pressure and energy is released. This release of energy, is what causes the unstable atom to split to an isotope. I hope this helps!]
[isotopes can split too. At least some.]
Explanation:
Imagine you are trying to push something heavy, fusion is how you can join together and help each other to push this heavy material.
Fun fact! Heavier materials have more inertia against other forces acting on them.
You push harder, harder and harder! Until its pushed.
This will release a lot of energy which escalates to an extended length.
It might not be the finest example, it helped me to understand the basics.
Fission. Imagine having so much energy, in this case, try thinking of so many people in a tight space. What do you do? You will eventually start to escape and leave the room. This is the act of splitting the atom.
This won't be the same than how it was before.
Again, Energy is released (energy!!).
For anyone struggling with this, although it might not be the best idea, I would recommend researching the more advaced options for this topic.
This will give you a wide range of information which can develop your current knowledge about, "Nuclear Fission and Fusion."
It will be difficult, it definitely was for me when I was a child (starting to study science).
Just keep trying, you'll get it.