For a while now, I have been using Stackoverflow as a reader, not a user. But, since recently I started helping others out too. And you would be surprised to see how much you can actually learn from Stackoverflow. I am going to demonstrate this to you how I am learning while I am helping others.

1. First of all, register an account on Stackoverflow if you have not already. You can also login with facebook / openID or Google: http://stackoverflow.com/users/login
2. After that, you go back to the homepage and set some favorite tags, and some Ignored Tags. This will help Stackoverflow to highlight the questions which are relevant for you.
3. Once you have done this, the fun starts. There are a couple of ways to find questions relevant to you, I usually prefer the homepage. This is also quite a challenge as many people are watching the questions. You will have to answer within a minute or 2 (usually) to be the first to answer. But be sure you also answer the question correctly, and well formed so the one who asks the question can actually use your answer.

Well how about the learning? Quite easy. Just try to answer questions on which you are sure you should know the answer. This way, you will have to look for the answer yourself. Usually a short search on Google gives you the correct answer (and demonstrates how bad most people are in searching on Google).

If you are unable to locate the answer, someone else probably will. Just keep a watch on the question, or mark it as favorite (so you can look it up later on your profile page). This way, either way, you will learn from a question which you probably didn’t even ask yourself.

But now you know, and a next time you see a similar question, you know how to answer it.

But next to questions about stuff you actually do (in my case PHP/MySQL/JavaScript) you might encounter websites, technologies, etc, which might even give you new insights, or new ideas.