Compound interest is an investing term. The term also applies on general life. The principle means that the profit you make can be used to reinvest. Next time you receive a higher profit, you reinvest it and it keeps building on itself.
Take a look at studying a certain subject. When learning something new you aren’t jumping in to the most difficult part of it, but slowly getting to know it. For example learning a new language. You start with learning how to greet someone, how to ask questions, how to answer to them, and so. The more you learn the more you can add and the easier you can speak and understand others. My English is far from perfect, but the only way of ever writing these articles is by compounding what you learn and to keep improving.
Skill is the unified force of experience, intellect and passion in their operation. – John Ruskin
The people around you who are successfull have reached that stage by focussing their work on the skills they need the most. They collected experience in that area and created a passion to learn. Only with enough practice and experience you will continue to improve. Once certain knowledge is acquired it is possible to implement it in a different area. For example you might be a Spanish teacher in the United States, if you add French to your knowledge you can teach Spanish to French speaking people. A different example is if you work in a company providing IT support to help the other employees. Your employer will certainly appreciate if you have some experience in cyber security. It may not be required for your job, but it never hurts to add it as a new skill.
Experience in a certain skill also allows you to improve a different skill. For example you could be working as a nurse in a hospital doing good work. However the better you learn to understand people, to calm them down potentially even in their own language, the easier their recovery will be. If you are working a specific job where either the job description or your employer doesn’t value your extra skill don’t give up on it. You may not have a benefit from it right now, but you can get profit from it later in life. An example of an unusual skill is learning to drive anywhere, anytime, without GPS. Nowadays everyone uses GPS because of the easy access and user-friendliness. Your knowledge of finding your way anywhere will benefit you in the long run.