Your Web Address is the website URL where you have uploaded the 'oneadmin' folder and files. In other words, it is the full URL to access your One Admin panel.
You may need the Web Address to request for your product activation key. It is defined in your 'config.php' file by the Installation Wizard with the $path["webroot"] variable. If required, you can modify the Web Address by editing the 'config.php' file.
Please make sure that you include a '/' at the end of the URL as shown above.