Understanding means to comprehend, or the ability to mentally grasp the significance or nature of a concept or information of what is or was being taught or conveyed.
OK, so now that we are clear on the meaning of understanding, my next question is, why do we need to understand?
We want to understand because we are interested, instinctively in what is going on around us. Understanding is a learned process that we are inherently fortunate to have. It is a tool that lets us search for explanations and to comprehend them. Once we understand something, we can build on that and understand even more. This is how we learn and make progress. Our knowledge is constantly expanding if we continue to search and if we are curious. If we stop searching, we tend to stagnate and start to cease developing, but our knowledge is retained in long-term memory. As long as we have questions, we will be looking for answers, and we will seek to understand those answers.
To comprehend, we must know and apply what we have learned and that that knowledge has some use or meaning for us. We must get the concept that is trying to be communicated or conveyed. When it makes sense, and you really understand and can explain what it means, then you would be able to teach it to another person if you had to and can explain the ways and how to apply it to real-life or in theory.