Search for words or phrases that would appear in the Subject line of a message. This is not the thread name as seen and searchable from the main forum page, but the titles of the individual messages within a thread. This is also a "contains" search. Again be careful of searches that are too general.
Search for a particular person that has posted. This is also a "contains" search, so searching for "Max" will also yield "Max D. Spiegel" and "Max Spiegel", "Alan Lomax", etc., but searching for "Max D. Spiegel" will not produce any "Max" enties.