As a Pipedrive customer, you should have a custom domain like https://mycompany.pipedrive.com. Enter the mycompany.pipedrive.com part in the extension's preference under Domain.
Find your user's Pipedrive API token in your preferences on the Pipedrive website, then save it in the extension's preference under API Token.
If you need help finding your API token, Pipedrive has some documentation here.