Literally speaking an internet forum is a place where people hold discussions regarding a predetermined topic in form of posted messages. People use forums to express their opinion, share ideas and get perspective of one another on the same topic.
Now add programming affix to a forum and you get an online forum where programmers and developers gather to discuss their ideas about the latest piece of software they have come across, articles regarding their line of work, questions and answers which would benefit newbie programmers, tips, trick and techniques and source code.
Programming forums are an indispensable source of information for both the newcomers and old veterans in the world of programming who want to update their knowledge banks with the latest advancement in the world of software development. It is a great place to seek out help if you are having difficulty with a rather tricky piece of code that you are trying to write or want to get an opinion on some development recently done.
The internet has an abundance of programming forums which have senior programmers contributing to them regularly with expert opinion and advice. Like simple discussion forums which are categorized according to topics like food, health, culture, religion and politics, a programming forum is classified according to which programming technology is being discussed.
It is not uncommon to find programming forums dedicated to a specific programming language, for example like Sun Studio's Java or Microsoft's Dot net platform, where discussion is restricted to topics relating to these languages. Other programming forums serve a broader horizon and include threads which discuss multiple programming languages and scripting languages like Perl, python and PHP.
It's just a matter of conducting a proper search and finding one, out of hundreds and thousands of programming forums littered across the internet, which has answer to your queries. Once you have found such a forum, all that required is to register and get yourself approved by a moderator.
Second step would be to seek out the thread which deals with the particular programming language you are interested in and simply start contributing with your two cents, seek help and advice by posting relevant questions or see what others have to say about it. Every forum, be it a simple discussion forum or a programming forum, has a certain predefined set of rules and regulations which are applicable to all those who are participating. Make sure to thoroughly read these terms and conditions beforehand and abide by them all the time. Most moderators are on the lookout for violations of these terms and conditions and may or may not without warning cancel membership and impose a ban on violators.
There are some programming forums which are sponsored or owned by companies which publish the programming language itself. For example, there could be programming forum for Microsoft's Visual Basic.net where the end user could discuss and interact with the very developers who produced the language. These programming forums are advertised by such companies and users are encouraged and sometimes rewarded for their contribution which may come in form of questions, healthy criticism or identifying a flaw.