No, you don't need a degree to understand whatever it is that you don't understand. Depending on the topic, you may need to do some research, ask questions, and/or practice to gain a better understanding, but a degree is not necessary. For example, if you don't understand a certain math concept, you can look up tutorials, ask your teacher for help, or practice solving related problems to gain a better understanding. Or, if you don't understand a certain concept in history, you can research the topic, ask your teacher for help, or read books on the subject to gain a better understanding. In any case, a degree is not required.
