There are a number of different forums on the internet covering the discussion of almost any topic imaginable. There are literally millions of different forums, but local forums are popular with many people and British people using forums will often favour a UK forum.
A UK forum will typically deal with topics specific to the UK or that affecting people living in the UK. Very large internet forums which cover a nonspecific topic will often have a smaller UK forum or sub forum allowing people who are interested in the topic based in the UK to discuss it with other people from the UK. Many large international forums will have specific sub forums for people from certain countries, or people who speak a certain language.
It is typically for most online forums to require their users to register their email address and details in order to post, however many users do not register and simply browse the forum instead of posting, a practice which is colloquially referred to as lurking. There are also a number of online forums that do not require registration where users can post anonymously, however many people believe that the quality of the posts of these types of forum will typically suffer due to forced anonymity.
A UK forum or any online forum for that matter is often a very useful place to access information, particularly when a forum specialises in a certain topic. Many enthusiasts and experts visit forums that are specific in their area of expertise.