And you can conduct a search from either the main page, from within a Forum, or within a specific thread, in which case the Search link only searches that thread.
If you chose to search from either the main page or from within a Forum, you have some additional Search options -- for example you have an option to search either Threads or Posts. I find that with common or broad search subjects, it's much easier to find what I'm looking for if I search Posts rather than Threads, because a Thread can have many, many posts, and finding the specific thing I'm looking for can be quite time consuming.