From the FAQ
How do I search for something?
To quickly find a thread or post of interest anywhere on the bulletin board, click on the 'Search' link in the navigation bar at the top of most forum pages. Then, type in the keyword or phrase you wish to search for, and select either 'Show Threads' or 'Show Posts' to view the results. By selecting posts, you will be shown only the actual post in which the search word appears.
For more control over the search, select 'Advanced Search' from the drop-down box. The advanced search page allows you to restrict your search to individual forums, find posts or threads by user, or return results based on tags ***. There are also options to find posts from a certain date, or threads with a certain number of replies.
How do I search a specific forum or thread?
If you are browsing a forum, you can quickly search for a thread or post within it by clicking on the 'Search this forum' link near the top of the page (it's above the list of threads). You can also search for individual posts within a thread by clicking on the 'Search this Thread' link at the top of any thread view page.
What are tags?
Tags are a useful way to search for threads with similar subject matter and content. This complements the normal search system, which searches only for certain words or phrases and/or posts by specific users.
To use tags, you add words or phrases to threads to help describe the content. For instance, if the subject matter is 'photography' then you can add the tag 'photography' to the tag list. But you could also add tags like 'digital image', and 'camera' (depending, of course, on the nature of the thread).
This will categorize this thread with all other threads that have matching tags, whether or not they have the word 'photography' in them.
Who adds the tags?
Tags are initially added to threads by the user who started the thread. Other users may also be able to add and remove tags.
How do I use tags?
Tags are displayed in a box near the bottom of a thread page. Clicking on a tag will allow you to view other threads that have the same tag - and which may be related. Clicking on the word 'Tags' in the top of the box will take you to an overview page with a 'tag cloud.'
This cloud allows you to see which tags are the most popular - the larger the word, the more times it has been used on threads within the board. There is also another tag cloud on the advanced search page that shows you the tags that have been searched for (or clicked on) the most.