Start typing in the header and you get a short list to jump straight to something. Press enter for the full results page, where you can narrow by what kind of thing it is, who wrote it and which forum it was in.
Search only ever returns things you are allowed to see. A private forum or a club you are not in will not appear, and that includes its titles.
Two or three distinctive words work better than a sentence. If you remember a phrase somebody used, search that rather than describing what the thread was about.