To use Poodll you will need to have a Poodll subscription (free trial is ok) and your Poodll API username and secret. You can get those from the "API Creds" tab in your members area on https://poodll.com/member/?action=api . Your API username is the same as your username on https://poodll.com.
If you have not registered your Moodle site URL you will need to, so that Poodll can authorize it. Register your URLs at the bottom of your member page: https://poodll.com/member .
The registration code that is generated there is an alternative and older way of registering Classic Poodll (the Poodll filter). It is not needed for Cloud Poodll or Classic Poodll any longer, but users on older Poodll versions and intranet only servers may still need to use it.
There is no need to update your API key after registering new URLs, subscription renewals or upgrades.
You can generate a new API secret by pressing the "Fetch new API secret" button. But note that you will then need to update it anywhere you have been using the old secret.