Installing btnx and btnx-config should have created a menu entry in your system. GNOME users can find it under . In KDE, the menu item is located at . Click on it to start btnx-config.
If, for some reason, the menu entry doesn't exist or the program doesn't start, try starting btnx-config from the command line as root:
# btnx-config
You might get some warning messages, but don't worry about them if the program works. If you get errors and the program doesn't work, see the Troubleshooting section.
Once btnx-config has started correctly, the window below is shown.

btnx-config startup screen (as seen in GNOME)
At this point, no mouse or buttons have been detected. You will have to detect them before defining their functionality (see "Detecting the mouse" and "Detecting buttons" sections).