The App Key is generated automatically once the V4S Mobile app is installed in the Salesforce org.
A new App Key must be generated only if there are multiple locations where the volunteers volunteer in your org and need a different configuration set up in each location. Different App Keys can be created and filters can be added to each App Key using the V4S Mobile configuration screen.
To create a new App Key, go to V4S Apps Tab in Salesfroce and click the new button. Enter a proper name to recognize the App Key and click the Save button. And a new App Key is generated, click the all view in the V4S Apps tab to see the new App Key.