QQSearch is... hard to define. It's a search engine (OpenSearch compatible!) which uses other search engines. But it also serves as a convenient bookmark keeper, if the search assist functionality isn't used.
Mostly, it works like a private version of yubnub, meant for people who want to keep their (search) bookmarks private, and/or to keep a historical record of their searches (the author notes, as of 2011-06-22, he had 5488 search queries archived since 2009-07-13).
The magic behind using QQSearch as a search engine is mostly as simple as knowing how to form a search URL. When adding a URL mapping to QQSearch, one can use placeholders to be filled in on later use (see also "help add" in your new install of QQSearch).
For example, a Google search URL looks like this:
http://google.com/search?q=search+terms+go+here
Because you know where the search terms go, you can add a google search to your QQSearch using {{*}} as the placeholder for them:
add google http://google.com/search?q={{*}}
Now, when you type
google you're a good man charlie brown
into QQSearch, it knows to translate that to
http://google.com/search?q=you're+a+good+man+charlie+brown
and sends you straight there after translation (storing the query in its search history while it's doing that).
Now, QQSearch doesn't really care if it's sending you to a search URL or any other kind of URL. A URL is a URL is a URL, ad infinitum. So, you can do some really clever things. For instance, have you noticed that twitter URLs generally look like this:
http://twitter.com/username
You could therefore give yourself a shortcut to practically any Twitter user, as long as you knew their @name:
add t http://twitter.com/{{1}}
And you could use that to quickly jump to, for instance, @notch's twitter:
t notch
Which immediately gets translated to:
http://twitter.com/notch
Finally, by hosting QQSearch on an Internet-facing machine (though not an insecure one!), you can have the same bookmarks and search shortcuts from any computer connected to the Internet -- and aggregate the search history from all of them in one place!