Press the search button or CTRL-S to bring up the search dialog for the currently selected hub (click on a hub tab to select it). You can have several search dialogs open at one time, one for each connected hub.
The search dialog consists of some controls for searching, and a result window. The result can be presented as either an ordinary list or in a tree-like form. Click on the "list view" and "tree view" tabs to select which one. Both views has their pros and cons, experiment with them to get a feel for when to prefer one over the other.
Search strings are typed into the text field labeled "Search". Typing a space between words makes dc-qt search for the exact string. A $ instead of space means "and". Better handling of this will be added in the next release. If you are searching for a certain type of file, music for example, select it from the "type" drop-down box. You can also limit the number of search results by specifying the size to be at least or at most a given value, although this is not required. Click the "Search" button to search on the current hub, or click "Multihub" to search on all connected hubs. Search results from other hubs will show in their respective search dialogs. Therefore, when using the multihub search, you may get some new search dialogs popping up. This may not be the best approch, but it lets you distinguish between search results so that you always know on which hub a certain file was found.
You can download the same file from several users at the same time, making the download faster in some cases. Right now, you must manually add the sources for a file by double clicking on the files, in the future this will be automated.
You can also download whole directories or download to another directory than the default. The menu that pops up when right-clicking provides these functions.