How does an understanding of energy, help scientists explain phenomena in
all fields of science?

Energy is if not the most fundamental unit of everything, along with matter, space and time, thus it is one of the foundations of all science.

Explanation:

Energy in science is like words in a book, you could not read the book without words, similarly, there would be no way to do science without energy. Take this example You can only measure the *speed* of an object if it has energy.

We could look at biolgy and see how photosynthesis makes use of energy. In photosynthesis we see plant cells converting energy from the sun into usful sugars to help the plant grow.

Now we could look at astronomy and see how energy is used, If you observe stars you can see the different brightnesses and masses, which tells you alot about what type of energy conversion is happening inside the star (nuclear fusion).