The wise have said it all along: The best way to show that you’ve mastered something is to teach it to someone else.
Even if “mastered” sounds too exalted, the idea holds true. However modest your knowledge, there’s someone out there with less. So when you see a chance, pass it along! In the process, you’ll better organize the knowledge in your mind, and you’ll realize any remaining questions that you want to research. In the end, you’ll cement that knowledge into something as durable as – well, cement.
You may not have much chance to help others right at the keyboard. That’s all right; on the Internet, you have infinite opportunity to help others online. In addition to answering friends’ questions by email or other means, you can jump into forums where people ask questions. Go to forums to learn, but try to give in return: When you see a question you can answer, jump in and do so.
This site is a perfect place to do this. Drop by to ask, to learn, and to teach. Everyone’s welcome, even with the questions you thought were too dumb to ask!