The query form "Code Query" at the top of the front page shows the path on a typical Wii SD card, where each title's folders can be found (consider "SD:" as your SD card slot's drive letter):
The text field can accept the folder names in the /title/ folder as the game codes. It will also accept truncated codes, such as the system identifier (E.G. S) or a title code with an unknown encoding (E.G. R4C). It will even recognise hexadecimal title codes.
The query form also includes a checkbox to show game titles in their original language. If these titles do not display correctly, you may need to manually set your browser's character encoding to Unicode (UTF-8).