Run the InitializeOAuth choreo, specifying the Client ID and Client Secret from the app you registered at Dwolla and the desired Scope. The InitializeOAuth choreo will return an authorization URL and a callback ID (required for the FinalizeOAuth step).
Open a new web browser, navigate to the authorization URL returned by the InitializeOAuth choreo, and click "allow" to grant the app access to your Dwolla account.
Run the FinalizeOAuth choreo, specifying the callback ID returned earlier by the InitializeOAuth choreo, to obtain an OAuth access token that can be used to access the Dwolla API.
When an Access Token expires, you can run the Dwolla > OAuth > RefreshToken Choreo providing the Client ID, Client Secret, and Refresh Token (also returned during the OAuth process) to retrieve a new Access Token and Refresh Token pair.