After downloading, open the disk image and double click on the preference panel. You will be asked whether to install for all users or just the one currently logged in. Next you should see a message that HIDden is not running, and offering to launch it for you (hint: click the launch button).
You should see a window like this:
First, note the "Start HIDden at Startup" check box. Checking this will add a reference to HIDden to the Login Items, which you can verify in the Accounts preferences in the System Preferences. The actual HIDden applicition is stored in the Resources folder of the just installed preference pane.
Second, you need to be careful with the "Seize All Input of Device" checkbox.
With this option off (unchecked), the controls (key presses) are 'heard' by HIDden, but also the rest of the system. Take the mute key as an example: OS X does respond by muting the system volume, but you can specify HIDden to do an additonal action, like hiding DVDPlayer, when that button is pressed.
The Pop-up Menu lists all devices (keyboards, mice, joysticks, etc.) found. Select the one for which you want to edit preferences. Note that some devices seem to appear twice. My keyboard has two components, a Generic Desktop-Keyboard part and a Consumer-ConsumerControl part. This is good! You could have HIDden seize just the Consumer part, and let the Keyboard part pass to the system. (Note: Here it can be confusing because the function keys (F1, F2, ...) can be controls of both parts, depending whether F-Lock is activated.)
Tell HIDden to listen to the selected device by checking "Listen to Device."
So there's a list of controls that were discovered by HIDden, but which one is the little "Webcam" (for exmaple) button? Well, press that button and the list should jump to the corresponding control! On my keyboard, it is called Button 2, which the sytem interprets as a right-click (here is an example where "Seize All Input of Device" is useful.)
Once you knwo which control corresponds to which button, you can specify what action you want to trigger, or "No Action." Some advice here: