This is a page where you can enter your registration information once you've purchased the PRO version.

To do this, press the “Enter registration key” button.

Enter your user name and license key into the corresponding boxes and press OK.

After you enter your registration information the Spider Player PRO page will change to something like this.

You will also notice changes in the “About Spider Player” window, which mean you've just successfully registered Spider Player and unlocked all the PRO features.