Stack Overflow is one of the most wonderful site a software professional should know about as it helps in solving many issues. This site is especially designed for programmers to ask any queries related to programming.
You should register with this site and you can ask and answer the questions that you know very well about particular query or language. I have been a member of this site for the past 1.5 years and I ask for solutions of complex problems in java, hadoop and mongodb etc. Its really helpful for programmers.