The difference between knowing and understanding shows up the moment the question is worded differently.

Knowing something is being able to produce the answer to a familiar question. Understanding is having the thing itself, so you can still find the answer when the wording moves, the numbers change or the problem arrives from a different direction. The two feel identical while you are studying, which is why rewording is such a reliable test. One survives a surprise and the other does not.

After you learn something, restate the problem in your own words and solve a version you have not seen. Invent a question about it and answer that one.