You do not have to configure kreXX. It works very well out of the box. There are two ways to configure kreXX:
Edit configuration file settings in the backend
Edit local cookie settings in every debug output
The editor for the configuration file can be found on the second tab of the backend module.
The toggle button on the right will enable the setting. The info button onm the right will display a short description about the specific setting. To save the desired configuration, simply click on the save button on the top.
When a previous setting was stored, but later reverted, the backend will remember the last setting and offer it. This is especially useful for the IP-Range.