Here's how you do it. Let's say I'm looking for Godsmack - I Stand Alone, off the Scorpion King album (Obviously, if I know what album it's on, or what artist or whatever, it's faster to just go directly to it. But let's say I've searched all of my Godsmack albums and it's not there. I've forgotten that it was on the Scorpion King soundtrack, so I'm searching.).
The first thing I do is go to Audio. My default Audio view scheme is Album Artist (auto)/Album. So I have a list of Album Artists. I know it's Godsmack, but I also know that there I have no Godsmack album with this particular song on it, so rather than just choose Godsmack out of this list, I choose All. When the menu opens up, I choose Search.
At this point I now have a list of letters, a-z mostly likely, although there might be a few missing here and there. These represent the first letters of all the songs that are here. I'm looking for "I Stand Alone" so I choose "i" from the list and choose Open.
Now I have "i" followed by a bunch of other letters. "i_", "ia", "ib", "ic", etc. I'm looking for "I Stand Alone", so I choose the "i_" option (the _ signifies a space).
Now I have options like "i a" "i b" "i b" etc. So now I choose the "i s" option. Then "i st", followed by "i sta" etc. etc. until I get to "I Stand Alone". At any time, I can choose to "Show Files" rather than "Open" in order to end the search and just see the list of results.
The one thing I'm not clear on is which fields it actually searches on. In the example above, I could either search for Godsmack or just I Stand Alone and find the file I was looking for. It doesn't seem to handle Genres though, so I'm unclear as to just which fields are included in the search.