The famous Nobel winning physicist Richard Feynman understood the difference between "knowing something" and "knowing the name of something" and it’s one of the most important reasons for his success.
Teach it to a child
Take out a blank sheet of paper and write the subject you want to learn at the top. Write out what you know about the subject as if you were teaching it to a child. Not your smart adult friend but rather an 8-year-old who has just enough vocabulary and attention span to understand basic concepts and relationships.
A lot of people tend to use complicated vocabulary and jargon to mask when they don’t understand something. The problem is we only fool ourselves because we don’t know that we don’t understand. In addition, using jargon conceals our misunderstanding from those around us.
When you write out an idea from start to finish in simple language that a child can understand (tip: use only the most common words), you force yourself to understand the concept at a deeper level and simplify relationships and connections between ideas. If you struggle, you have a clear understanding of where you have some gaps. That tension is good –it heralds an opportunity to learn.
Review
In step one, you will inevitably encounter gaps in your knowledge where you’re forgetting something important, are not able to explain it, or simply have trouble connecting an important concept.
This is invaluable feedback because you’ve discovered the edge of your knowledge. Competence is knowing the limit of your abilities, and you’ve just identified one!
This is where the learning starts. Now you know where you got stuck, go back to the source material and re-learn it until you can explain it in basic terms.
Identifying the boundaries of your understanding also limits the mistakes you’re liable to make and increases your chance of success when applying knowledge.
Transmit
If you really want to be sure of your understanding, run it past someone (ideally who knows little of the subject –or find that 8-year-old!). The ultimate test of your knowledge is your capacity to convey it to another.
A source